A membrane-surface liquid culture (MSLC), in which microorganisms were grown on a microporous membrane surface exposed to the air with the other side of the membrane in contact with liquid medium, was applied to the production of neutral protease from Aspergillus oryzae LAM2704. The amount of protease produced by batch MSLC was much higher than that produced by shaking culture, liquid-surface culture, or agar plate culture. In MSLC the amount of protease produced per milligram of dry cells as well as the amount of protease produced were dependent particularly on the glucose concentration. By decreasing the glucose concentration from 1.5% to 0.2%, the amount of protease produced and its specific amount were increased by 60% and around 7 times, respectively. Using a medium containing 0.2% glucose and 0.4% casein, long-term repeated-batch production of the enzyme was conducted by exchanging the medium every 12 to 48 h with a fresh one. Protease production continued in more than 15 successive batches, although the amount of enzyme produced in each batch gradually decreased. When the medium was exchanged every 24 h, the degree of the decrease was the smallest, and the cumulative amount of enzyme produced was more than 20 and 400 times those obtained in the batch MSLC and shaking culture, respectively.