Undesirable protease production by Aspergillus niger Aa-20 in submerged culture and solid-state culture was evaluated using different concentrations of tannic acid as sole carbon source in a model system designed for tannase production. Protease production was found to be dependent on the culture system used (submerged culture or solid-state culture) and on the initial tannic acid concentration. Expression of protease activity in submerged culture was higher (up to 10 times) than activity obtained in solid-state culture, using identical culture medium composition. In submerged culture, the lowest final protease activity (0.13 IU) was obtained with the highest tannic acid concentration, while in solid-state culture protease activity was not affected by changes in initial substrate concentration. Absence of detectable proteolytic activity in solid-state culture is related to high production of tannase enzyme. Hence, the use of solid-state culture for fungal enzyme production may allow for higher and more stable enzyme titers present in culture extracts.