Abstract: Objective To study the toxic effect and the change of permeability on human umbilical vein endothelia (HUVE) of the Loa22 protein from virulent serovar Lai.\Leptaspira interrogans by expressing its protein. Methods In this study, the pGEX-Loa22 peptide prokaryotic recombinant plasmid of \Leptaspira interrogansserovar Lai preserved in our laboratory was used to express Loa22 fusion protein with GST lable. Then the target fusion protein was obtained by using affinity chromatography with the GST-Trap FF Column. The purified Loa22 fusion protein was detected by SDS-PAGE and confirmed by Western blot assay using the mouse anti-GST tag monoclonal anti-body. pGEX-Loa22 protein was administered to culture with human umbilical vein endothelial cells (HUVEC) to elucidate the cytotoxic role and the change of permeability of leptospiral outer membrane proteins. Results The recombiant plasmid with Loa22 mature peptide was expressed successfully and the protein was purfied. Significant higher level of apoptosis ratio, lower CCK-8 aborntion, and increasing permeability on HUVEC were observed after treated the HUVEC with the expressed fusion protein. Conclusion The purified Loa22 fusion protein have obvious toxic effects on vascular endothelial cells, and also it can increase permeability of HUVEC.