The effect of some organic compounds on the activity of chitinase from Serratia marcescens has been investigated. Among these compounds, 1,10-phenanthroline was found to be an inhibitor and ethanol - an activator of the chitinase activity; - ’ dipyridyl and Zn2+ do not take any effect on the chitinase activity. In this investigation, the dissociation constant of an chitinase-metalic ion complex (K1) and the inhibition constant (K2) have been estimated with K1 = mcM and K2 = mM.