Sapium sebiferum is one of the most important oil trees.SAD(stearoyl-acyl ACP desaturase) protein is a dehydrogenase,which is a key factor for transforming saturated fatty acid to unsaturated fatty acid in oil plant.We expressed and purified SsSAD from Sapium sebiferum in E.coli to investigate its function.The result suggested that:(1)The full length cDNA encoding SsSAD was amplified by RT-PCR from Sapium sebiferum and cloned into cold shock inducible expression vector pCold TF.The recombinant prokaryotic expression plasmid was transformed into E.coli BL 21 star (DE3) strain for gaining of the genetic engineering strain.(2)The transformed strain was induced with IPTG(isopropylthio-D-galactoside)for expressing fusion protein at low temperature.Results showed that the recombinant protein with a molecular mass 101 kD was highly expressed in E.coli and present both in the supernatant and the pellet part of E.coli lysates.The supernatant was further purified by affinity chromatography and detected by Western blotting,which demonstrated that high quality recombinant protein was obtained and laid the foundation for investigation on the structure and function of SsSAD.