Abstract: The optimizied expression of the cloned Cyclodextrin glycosyltransferase( CGTase) Gene in Escherichia coli strain BL21( DE3) induced by lactose was reported. By comparing the influence of lactose and IPTG on the expression amount of the cloned CGTase,the induction mode was optimized.The genomic DNA of Geobacillus sp.CHB1 was used as template and the CGTase gene was amplified by the PCR technology. The secretory plasmid p EASY- E2- Omp A- cgt which contained the signal peptide Omp A of E.coli was constructed. The recombinant plasmid was transformed into E.coli BL21 and then induced to express.The expression level of the target protein in the shake- flask cultures induced by IPTG and lactose were analyzed by SDS- PAGE and meanwhile the extracellular enzyme activities were measured.The factors including inducer concentration,induction time,induction temperature and induction method were optimized. The CGTase gene was successfully expressed in E.coli BL2 l,and a certain amount of recombinant CGTase were secreted into the culture medium.The expression amount of the cloned CGTase induced by lactose was more than that induced by IPTG and the amount of inclusion body was less than that induced by IPTG.The optimal conditions for extracellular expression were as follows: 0.5% lactose,initial concentration of E.coli with OD600= 1.4 and the temperature with 25 ℃. There was no significant difference in the expression amount between addition of lactose in batch and one time. Under this condition,the extracellular activity reached 19.87 U / m L.The extracellular expression of CGTase gene from Geobacillus sp.CHB1 in E.coli BL2 l was achieved.Lactose could be used as an inducer instead of IPTG for the expression of recombinant CGTase.