Objective: To observe the changes of serum amylase and isoamylases in acute pancreatitis with different severity. Methods: The mice models of acute edematous pancreatitis and acute hemorrhagic pancreatitis were developed and the activities of serum amylase and isoamylases were assayed. Results: The severity of pancreatic edema was significantly correlated with the activities of pancreatic isoamylase in mice with acute edematous pancreatitis. When the pancreatic injury became the serious, the total activity of amylase in the mice with hemorrhagic pancreatitis decreased but still remained 1.5 times as high as the level of the control, and the activities of AMYp were 5 times higher than that in the control. Conclusion: The activities of serum amylase and isoamylase reflect the severity of pancreatic edema in acute edematous pancreatitis. It might be more effective to determine the activity of AMYp than AMY in the patients with acute hemorrhagic pancreatitis.