Air pressure pulsation (APPSSF) was applied to produce alkaline protease by Bacillus pumilus AS 1.1625. When the amplitude of air pressure pulsation was 0.10 MPa, the period of air pressure pulsation was 1 h, with a moisture level of 65%, the enzymic yield obtained by APPSSF was 860 U/ml, namely 4300 U/g wheat bran. This was more than twice that produced by static solid state fermentation (SSF). Air pressure pulsation also overcame the problems in static SSF caused by higher moisture level and increased bed depth. The results illustrated that air pressure pulsation was an effective method to enhance transfers of mass and heat during SSF and could be applied more widely. (c) 2004 Published by Elsevier Ltd.