The effects of potassium halides KCl, KBr and KI on NADH:FMN-oxidoreductase-luciferase bioluminescent coupled enzyme system were studied. The influence of salt additions on bioluminescence intensity and bioluminescence light yield was investigated. The inhibition and activation parameters of the salts were calculated using their dependencies on concentration of the salts. The correlation between the inhibition of bioluminescence intensity and the halide mass was demonstrated: the inhibiting ability of the salts increases with the increase of atomic weight of the anions. The inhibition parameters increase and the activation parameters decrease, accordingly.