It was established, as a result of investigations of the alpha-L-rhamnosidase of Eupenicillium erubescens kinetic properties, that K(m) and V(max) for the corresponding synthetic substrate were 1.0 mM and 120 micromol/min/mg of protein, respectively. alpha-L-Rhamnosidase was also competitively inhibited by the reaction product- L-rhamnose, the inhibition constant was 5.2 x 10(-2) M. One could also observe the inhibition of alpha-L-rhamnosidase reaction in the presence of 10(-3) M of glucose. It was shown that the rate of enzymatic hydrolysis of nitrophenyl substrate was directly proportional to the concentration of enzyme, and the increase of the substrate concentration leads to the increase of hydrolysis rate. The substrate concentration being increased above the optimal one (5.0 mg/ml), the reaction rate decreases due to the formation of inactive enzyme-substrate complex FS2.