Abstract: The phopholipase A1 gene from Serratia marcescens PL-06 named pla A was cloned,ligased with p ET-22b(+) to construct recombinant plasmid p ET-22b(+)-pla A and then transferred to E.coli BL21(DE3).The engineered stains expressing phospholipase A1 was obtained,and named AP22. After subsequent indution by IPTG,lots of approximately 35 ku protein was detected in the fermented liquid by SDS-PAGE. This protein was in the same size with the expected protein. Selectioning phospholipase A1 enzyme activity as reference,by single factor and orthogonal experiment method,optimized induction conditions for phopholipase A1 expression were obtained as follows:ampicillin concentration 30 μg/m L,IPTG concentration 0.25 mmol/m L,inducing temperature 34 ℃,strain density OD6000.3 and induction time 4 h. Under the optimized conditions,maximum phospholipase A1 enzyme activity was observed to be 8.6 U/m L and increased by 43.3% than before.