The value of the critical surface tension(?(c.0)) of the polyolefin part calculated by Zismann plot was 26.1?dyne/cm. The surface state and the ?(c,0) of the polyolefin part were changed by solvent treatment. Polyolefin part was influenced by solubility parameter of a solvent, on the other hand the degree of change in the surface state was dependent on a surface tension of a solvent. When a surface tension of solvent is lower than ?(c.0) of the polyolefin part, the wettability of a solvent was good and the surface state was greatly changed. The adhesion strength of polyolefin part was greatly improved to as compared to that of the untreated one. As the ?(c,0) of polyolefin part was closed to the surface tension of the primer, the good adhesion strength was obtained for ?(c)/?(L,p) ?1.