diff --git a/include/picrin/pair.h b/include/picrin/pair.h
index 5fd18e62..0167f96c 100644
--- a/include/picrin/pair.h
+++ b/include/picrin/pair.h
@@ -13,6 +13,7 @@ int pic_length(pic_state *, pic_value);
 pic_value pic_reverse(pic_state *, pic_value);
 
 pic_value pic_assq(pic_state *, pic_value key, pic_value assoc);
+pic_value pic_assoc(pic_state *, pic_value key, pic_value assoc);
 pic_value pic_acons(pic_state *, pic_value key, pic_value val, pic_value assoc);
 
 pic_value pic_caar(pic_state *, pic_value);
diff --git a/src/pair.c b/src/pair.c
index 193d4c77..83ac92d6 100644
--- a/src/pair.c
+++ b/src/pair.c
@@ -128,6 +128,24 @@ pic_assq(pic_state *pic, pic_value key, pic_value assoc)
   goto enter;
 }
 
+pic_value
+pic_assoc(pic_state *pic, pic_value key, pic_value assoc)
+{
+  pic_value cell;
+
+ enter:
+
+  if (pic_nil_p(assoc))
+    return assoc;
+
+  cell = pic_car(pic, assoc);
+  if (pic_equal_p(pic, key, pic_car(pic, cell)))
+    return cell;
+
+  assoc = pic_cdr(pic, assoc);
+  goto enter;
+}
+
 pic_value
 pic_acons(pic_state *pic, pic_value key, pic_value val, pic_value assoc)
 {