diff --git a/nac3core/src/toplevel/composer.rs b/nac3core/src/toplevel/composer.rs
index bf9f1561..152094d2 100644
--- a/nac3core/src/toplevel/composer.rs
+++ b/nac3core/src/toplevel/composer.rs
@@ -1065,10 +1065,23 @@ impl TopLevelComposer {
                             and names thould not be the same as the keywords"
                                 .into());
                         }
-
-                        args.args
+                        
+                        let mut arg_with_defualt: Vec<(&ast::Located<ast::ArgData<()>>, Option<&ast::Expr>)> = args
+                            .args
                             .iter()
-                            .map(|x| -> Result<FuncArg, String> {
+                            .rev()
+                            .zip(args
+                                .defaults
+                                .iter()
+                                .rev()
+                                .map(|x| -> Option<&ast::Expr> { Some(x) })
+                                .chain(std::iter::repeat(None))
+                            ).collect_vec();
+                        arg_with_defualt.reverse();
+
+                        arg_with_defualt
+                            .iter()
+                            .map(|(x, default)| -> Result<FuncArg, String> {
                                 let annotation = x
                                     .node
                                     .annotation
@@ -1120,7 +1133,12 @@ impl TopLevelComposer {
                                 Ok(FuncArg {
                                     name: x.node.arg,
                                     ty,
-                                    default_value: Default::default(),
+                                    default_value: default.map(|default| {
+                                        match Self::parse_parameter_default_value(default) {
+                                            Ok(res) => res,
+                                            Err(err) => panic!("{}", err),
+                                        }
+                                    }),
                                 })
                             })
                             .collect::<Result<Vec<_>, _>>()?
@@ -1272,7 +1290,20 @@ impl TopLevelComposer {
                         }
 
                         let mut result = Vec::new();
-                        for x in &args.args {
+                        
+                        let mut arg_with_defualt: Vec<(&ast::Located<ast::ArgData<()>>, Option<&ast::Expr>)> = args
+                            .args
+                            .iter()
+                            .rev()
+                            .zip(args
+                                .defaults
+                                .iter()
+                                .rev()
+                                .map(|x| -> Option<&ast::Expr> { Some(x) })
+                                .chain(std::iter::repeat(None))
+                            ).collect_vec();
+                        arg_with_defualt.reverse();
+                        for (x, default) in arg_with_defualt {
                             let name = x.node.arg;
                             if name != zelf {
                                 let type_ann = {
@@ -1317,8 +1348,15 @@ impl TopLevelComposer {
                                 let dummy_func_arg = FuncArg {
                                     name,
                                     ty: unifier.get_fresh_var().0,
-                                    // TODO: default value?
-                                    default_value: None,
+                                    default_value: default.map(|default| {
+                                        if name == "self".into() {
+                                            panic!("`self` parameter cannot take default value at {}", x.location)
+                                        }
+                                        match Self::parse_parameter_default_value(default) {
+                                            Ok(res) => res,
+                                            Err(err) => panic!("{}", err),
+                                        }
+                                    })
                                 };
                                 // push the dummy type and the type annotation
                                 // into the list for later unification
diff --git a/nac3core/src/toplevel/helper.rs b/nac3core/src/toplevel/helper.rs
index 35da97c9..836a739d 100644
--- a/nac3core/src/toplevel/helper.rs
+++ b/nac3core/src/toplevel/helper.rs
@@ -1,3 +1,8 @@
+use std::convert::TryInto;
+
+use nac3parser::ast::{Constant, Location};
+use crate::symbol_resolver::SymbolValue;
+
 use super::*;
 
 impl TopLevelDef {
@@ -341,4 +346,49 @@ impl TopLevelComposer {
         }
         Ok(result)
     }
+
+    pub fn parse_parameter_default_value(default: &ast::Expr) -> Result<SymbolValue, String> {
+        fn handle_constant(val: &Constant, loc: &Location) -> Result<SymbolValue, String> {
+            match val {
+                Constant::Int(v) => {
+                    if let Ok(v) = v.try_into() {
+                        Ok(SymbolValue::I32(v))
+                    } else {
+                        Ok(SymbolValue::I64(v.try_into().unwrap()))
+                    }
+                }
+                Constant::Float(v) => Ok(SymbolValue::Double(*v)),
+                Constant::Bool(v) => Ok(SymbolValue::Bool(*v)),
+                Constant::Tuple(tuple) => Ok(SymbolValue::Tuple(
+                    tuple.iter().map(|x| handle_constant(x, loc)).collect::<Result<Vec<_>, _>>()?
+                )),
+                _ => unimplemented!("this constant is not supported now at {}", loc),
+            }
+        }
+        match &default.node {
+            ast::ExprKind::Constant { value, .. } => handle_constant(value, &default.location),
+            ast::ExprKind::Call { func, args, .. } if {
+                match &func.node {
+                    ast::ExprKind::Name { id, .. } => *id == "int64".into(),
+                    _ => false,
+                }
+            } => {
+                if args.len() == 1 {
+                    match &args[0].node {
+                        ast::ExprKind::Constant { value: Constant::Int(v), .. } =>
+                            Ok(SymbolValue::I64(v.try_into().unwrap())),
+                        _ => panic!("only allow constant integer here at {}", default.location)
+                    }
+                } else {
+                    panic!("only allow constant integer here at {}", default.location)
+                }
+            }
+            ast::ExprKind::Tuple { elts, .. } => Ok(SymbolValue::Tuple(elts
+                .iter()
+                .map(|x| Self::parse_parameter_default_value(x))
+                .collect::<Result<Vec<_>, _>>()?
+            )),
+            _ => unimplemented!("only constant default is supported now at {}", default.location),
+        }
+    }
 }