Two chymotrypsins were purified from the hepatopancreas of grass carp (Ctenopharyngodon idellus) by chromatographies on phenyl-Sepharose and Q-Sepharose. The molecular weights of chymotrypsins I and II were 28 and 27 kDa, respectively. The two chymotrypsins showed similar susceptibility to inhibitions by phenylmethylsulfonyl fluoride and soybean trypsin inhibitor, but differed in their response to tosyl-L-phenylalanine chloromethyl ketone and aprotinin in which chymotrypsin I was more resistant. Chymotrypsin I was a less typical chymotrypsin and exhibited lower catalytic efficiency with the chymotrypsin-specific ester and amide substrates, when compared with chymotrypsin II. For both chymotrypsins, optimal activity was detected in the pH range 7.0-8.5.