Abstract: Using one- step PCR, three amino acid residues Y127, R254 and D355 within the conserved protein domain of β- cyclodextrin glucosyl transferase were subjected to site- directed mutagenesis, and the mutant plasmids were transformed into Escherichia coli BL21 ( DE3) for effective expression, respectively. The result showed that the activity of mutant enzymes was 1.6 times higher than initial enzyme. The mutant enzymes were optimal at 60℃ and p H6.0, and that the enzymes were stable for at least 60 min at 60℃ and across a wide p H5.0~8.0, the enzymatic properties existed no significant difference among mutant enzymes and initial enzyme ( p > 0.05) , but there existed significant difference about activity between mutant enzymes and initial enzyme ( p < 0.05) .