We studied some mechanisms of cellobiase formation in Asp. japmiczls VKM F-2092 aiming at the subsequent development of controlled cultivation t o produce the enzyme. Formation of cellobiase was found to be of noninducible constitutive character. The enzyme was predominantly localized in the cytosole and the periplasm, its minor portion being cell-wall bound. The release of the enzyme into the medium was due to autolytic processes. The two-phaseness of cellobiase formation in Asp. juponicw grown on a mineral medium with 0.5% glucose was shown t o be determined by the following mechanisms: 1. Catabolic repression. We established glucose concentrations causing the repression and found it to be dependent on carbon sources in the growth medium. 2. Catabolic inhibition. Cellobiase activity was found to be inhibited by assumed glucose metabolites in the presence of nitrate nitrogen in the medium. Practical recommendations t o optimize the process of cellobiase production by Asp. japunicm are given.