Abstract: High purity monochloroacetic acid was prepared by catalylic chlorination of acetic acid with chorine by using acetic anhydride as the catalyst, and concentrated H2SO4 as the co-catalyst. The optimal conditions of synthesis were as follows: acetic acid /Cl2/ acetic anhydride / H2SO4 is 1︰1.26︰0.08︰0.008, reaction temperature from 100 to 105℃. The purity of monochloroacetic acid can be up to 99%. This method has the advantages of abundant supply of raw materials, simple process, and easy operation.