The effects of additives for food and drug upon the tryptic hydrolysis of casein an a Synthetic substrate, $N^{alpha}-Benzoyl-L-arginine$ ethylester (BAEE) in vitro has been studied. The results of this study were summarized as follows 1) It was found that the action of inhibition became stronger in the following order: Methyl parabene>Rose Bengal> Phloxine> Sod. DHA> Erythrosine by the colorimetric method using BAEE. These results also showed that other additives had no effect on the activity of trypsin. 2) All samples tested showed respectively same tendency using casein in this method. But the activity by Erythrosine and Sod. DHA was slightly increased in this experiment.