Outer membrane proteins (OMP) of Leptospira interrogans serovar lai strain 017 were extracted by using Triton X-114 (TX-114). The OMP were solubilized and phase partitioned into both the hydrophilic, aqueous phase and hydrophobic, detergent phase. TX-114 did not solubilize the protoplasmic cylinder in intact organisms. The protoplasmic cylinders contained a lot of protein bands and most of the TX-114 solubilized proteins partitioned into the aqueous phase, whereas only 14 protein bands entered the detergent phase with SDS-PAGE. Detergent phase proteins were of 5 major protein bands such as 66 kd, 39 kd, 35 kd, 27 kd, and 16 kd. Immunoblotting of the material extracted with TX-114 showed that detergent phase proteins of alone 39 kd was apparently immunoblotting with antiserum against such as whole cell of 017 strain the outer envelope of 017 strain and the immunoprotective anti-017 Mb E4B7G5. The results showed that we could separate and purify the 39 kd protein to analyse the amino acid sequence for the cloning, expression and development of genetic engineering vaccines.