The effects of orange peel, lemon peel, apple peel, wheat-bran and watermelon peel on beta-galactosidase production from Alternaria alternata were studied. Beta-galactosidase (EC-22.214.171.124) was produced best by solid-state fermentation of A. alternata on wheat bran. The effects of pH and incubation temperature were studied. The highest enzyme activity was obtained at 50 degrees C and pH 5.0. The enzyme was relatively stable in the pH range 3.0-5.0 and between 20 degrees-50 degrees C. The enzyme maintained 85% of its activity at 20 degrees-30 degrees C and 70% at 50 degrees C. Activity was more than 92% between pH 3.0-5.0 and 42% in 40 min and 50% in 30 min at 60 degrees C. In addition, glucose did not have an inhibitory effect, and galactose had only a slight inhibitory effect.