The acid protease gene in Saccharomycopsis fibuligera A11 was disrupted by integrating the HPT (hygromycin B phosphotransferase) gene into ORF (Open Reading Frame) of the acid protease gene. The mutant 12 obtained could grow in the medium containing hygromycin. No clear zone formed by the mutant grown on the plate containing milk protein was observed whereas a big clear zone formed by the strain All was detected. The acid protease and amylases activities produced by the mutant within 3 days were 0.89 U/ml and 424.7 U/ml, respectively while those produced by the strain A11 were 13.5 U/ml and 259.9 U/ml, respectively. The amylases preparations produced by the mutant 12 and the strain A11 kept 88.8% and 45.5% of amylase activity, respectively after they were incubated at 37 degrees C for two days. Trehalose amount accumulated in the mutant cells was 28.3% (w/w) while that accumulated in the cells of S. fibuligera All was 23.6 (w/w). (C) 2011 Elsevier Inc. All rights reserved.