The effect of electron-beam irradiation on enzymatic activities was studied with a crude enzyme preparation containing mainly glucoamylase [EC 3. 2. 1. 3] and α-amylase [EC 3. 2. 1. 1] from Rhizopus sp. strain Fukumoto. The liquefying and glucose forming activities of the crude enzyme preparation were damaged scarcely by the irradiation of 0.1-0.4 Mrad. But the glucose forming activity was damaged much more than the liquefying activity by the irradiation of 2 or 4 Mrad. Namely, on the glucose forming activities after irradiation of 0.4 Mrad, 2 Mrad, and 4 Mrad, relative initial velocities compared with control were about 97%, 84%, and 76%, respectively, and the residual liquefying activities after these treatments were about 98%, 97%, and 90%, respectively. The apparent Km value of glucose forming activity for amylose was not changed by irradiation of the crude enzyme preparation.