Elastase had broad application in food industry, medicinal industry and cosmetics industry. However, the stability of microbial elaslases was the greatest obstacle to affect its activity and efficiency. Based on this problem, this study is to investigate the acid mutation of Bacillus licheniformis ZJUEL31410 that produced elastase and to improve its acid-tolerant property and other characteristics. The methodology adopted was the simulated human intestine tract (low pH environment SHITES) The effects of different pH from pH 2 to pH 6 on elastase-producing strains were investigated. Experimental results demonstrated that S-4 mutant was the best stable and acid-tolerant strain considered the elastase activity and elastase stability under acid environment. It is evident that pH 4 is very efficient for improving the acid-tolerance of elastase and no negative effect on elastase activity. The secretion mode of the protein was analysed by SDS-PAGE. Experimental results suggested that the secretion mode of mutant under pH 4 was different from that of the control strain. The elastase characteristics produced by mutant strain were investigated and compared with the control. Results showed that B. licheniformis ZJUEL31410 strain was very stable under pH 6 and high temperature environment in comparison with the control and pH 2 strains. All of the aboved data indicated that the elastase produced by mutant strain was capable for practical industrial application. However, the mechanism supporting improved characteristics of elastase under acid-condition was needed to be investigated in the future research. (c) 2006 Elsevier Ltd. All rights reserved.