Abstract: OBJECTIVE To express the optimized alginate lyase gene aly-cob exogenously and optimize the expression conditions to achieve the high expression of alginate lyase. METHODS The alginate lyase gene from Cobetia sp. WG-007 was used to carry out rare codon modification， the recombinant plasmid pET-28a(+)-aly-cob was constructed and induced by isopropyl-β-D-thiogalactoside (IPTG) in Escherichia coli BL21 pLysS. Then medium components and the induction temperature， induction time， final concentration and adding time of IPTG was optimized to improve enzyme activity. RESULTS The recombinant E. coli BL21 pLysS/pET-28a(+)-aly-cob was constructed， the alginate lyase was induced by IPTG， and the optimum induction conditions were determined as follows: SB medium was the optimum medium， when the OD600 value of bacterial reached 1.0， IPTG was added with its final concentration was 0.1mmol/L， and after inducing for 24h at 22℃， the enzyme activity reached to 2403.93U/mL. CONCLUSION The optimized alginate lyase gene aly-cob is successfully expressed in E. coli BL21 pLysS and the expression conditions are optimized. The optimized enzyme activity is 15 times of wild-type enzyme activity， which is more favorable for industrial application.