As a natural inhibitor of trypsin, CHOM was purified from eggs and coupled with activated Sepharose 4B to prepare affinity chromatography media for purification of trypsin. Supernatants from cultures of two species of yeast were applied to the affinity chromatography columns. The activities of the purified products were detected. Results showed that some proteins with activity similar to that of trypsin really existed in the yeast culture. So it should be a good idea to add some trypsin inhibitor during culturing to improve the protein yield when yeast was used as a host to produce proteins.