We have studied on the applicability of the thermoplastic resins for GIS insulators. GIS insulators have been made of the epoxy mold resin. However, in recent years we should be careful to select plastics which are easily disposed and recycled. On this viewpoint, we selected some candidates of the thermoplastic resins, i.e. Polyamide, Polyacetal, and Poly-Phenylene-Sulfide to replace the epoxy mold resin, and evaluated these thermoplastic resins by several electric resistance tests. To examine the internal partial discharge resistance, we applied the CIGRE Method II test in which we modified the electrode arrangements. Poly-Phenylene-Sulfide had the longest lifetime in the test of internal partial discharge resistance, and worst property in the test of arc and tracking resistance. On the other hand, Polyacetal had a reversal tendency compared to Poly-Phenylene-Sulfide. As a result, thermoplastic resins showed enough characteristics in opposition to the epoxy mold resin in these electric resistance tests. The thermoplastic resins have possibility on replacement of the epoxy mold resin.