It is important to select effective and safe painting cleaning agent for mildew spots on mural paintings.Five biological and chemical cleaning agents5% trypsinase with dilute cleaning agent; 5% neutral proteinase with dilute cleaning agent; an ammonium hydroxide and ethanol mixture; and 70% ethanol in deionized water were applied separately to a simulated mildew board,cotton cloth used for removing and packaging of the mural painting and to the surface of mildewed Tang Dynasty mural painting.Cleaning experiments suggested that a biological agent,namely the trypsin solution,was effective.This,along with a few other chemical cleaning agents,can remove most of the mildew on the mural painting to be.