Abstract:The bound astaxanthin compounds in Procambarus clarkia shell was hydrolyzed to free astaxanthin with papain. The effects of four reaction parameters， including amount of papain， temperature， pH and time， on the yield of free astaxanthin were explored by the yield of astaxanthin as index. The optimal hydrolyzed con－ ditions was determined by the single factor test and orthogonal array design as follows： addition amounts of pa－ pain 10 %， temperature 45 ℃， pH 5.5， hydrolyzed time 5 h. Under these conditions， the yield of astaxanthin was 97.26 μg/g. In addition， pH had the largest impact on the yield of astaxanthin followed by temperature， hy－ drolyzed time and addition amounts of papain.