The effect of metal ions, surfactant, oxidizing agents and enzyme inhibitors was considered on trypsin and chymotrypsin activity of the Caspian brown trout fry. The results showed K⁺ and Na⁺ didn’t significanly decrease trypsin and chymotrypsin activity (p>0.05). Ca²⁺ and Mg²⁺ significantly increased trypsin and chymotrypsin activity (p<0.05). Mn²⁺,Cu²⁺,Ba²⁺,Co²⁺,Zn²⁺,Fe²⁺ and Al³⁺ significantly decreased the activity of trypsin and chymotrypsin (p<0.05). Saponin and taurocholic acid significantly increased trypsin and chymotrypsin activity. Sodium cholate significantly increased chymotrypsin activity (p<0.05), but not the trypsin activity (p>0.05). Oxidizing agents, including hydrogen peroxide and sodium perborate, significantly decreased trypsin (p<0.05). Trypsin and chymotrypsin activity significantly decreased in the presence of SBTI, PMSF and ρ-Aminobenzamidine inhibitors (p>0.05). The inhibitors such as TPCK, pepstatinA, iodoacetic acid, EDTA and ß-mercaptoethanol did not significantly decrease the trypsin activity (p>0.05), but they significantly decreased chymotrypsin activity (p<0.05). Trypsin activity in the presence of TLCK showed a significant decrease (p<0.05), but TLCK and pepstatin A had no significant effect on chymotrypsin activity (p>0.05).