The interaction of bovine liver arginase with hydroxylamine lead to decrease of enzymatic activity. The rate of inactivation increased at low pH (6.5-6.8). The inactivation kinetics and the concentration dependence have been investigated. The inhibition constant was estimated (K_i = 16 mM). The received data suggests that inactivation of arginase probably is result to the modification of carboxyl or carbonyl groups, which are involved in the active site of this enzyme or disposed near of it. The functional group with pK_a = 8.7 evidently take part in the interaction processes between arginase and hydroxylamine, which possibly keep up the modifying groups in the activated state. The fluorescence emission spectra of arginase upon excitation wavelength 280 and 297 nm were measured before and after the interaction with hydroxylamine. These results show, that there is no essential conformational changes in arginase macromolecule after hydroxylamine treatment, especially, in the region, where tryptophan and tyrosine residues are disposed.