The trypsin-inhibitory activity of the seven cultured f ish species, Ctenopharyngodon idellus, Carassius auratus, Hypophthalmichthys molitrix , Clarias fuscus, Aristichthys nobilis, Micropterus salmonoides and Monopterus albus were investigated. Individual f ish were bled and the trypsin inhibitory activity analysed using an arginine-aniline dye ester as clorimetric substrate. Results indicated the total trypsin inhibitory decreased from Ctenopharyngodon idellus through Carassius auratus , Monopterus albus, Aristichthys nobilis , Hypophthalmichthys molotrix, Clarias fuscus and Micropterus salmonoides with the lowest level. Analysis of the A2-macroglobulin actvity indicated a ranking w ith decreasing concentration of M. albus, C. idellus, C . fuscus , M. salmonoides, H . molotrix , A. nobilis and C. auratus. The results showed that M. albus had the highest A2-macroglobulin actvity, whereas C. idellus possess a higher level of trypsin-inhibitory activity than the other f ive species.