We report the physical characteristics of poly(vinyl acetate) (PVAc) as a polymeric gate insulator in the organic thin film transistors (OTFTs), in which the OTFTs require not only a simple packing process with a relatively low cost compared to conventional inorganic electronics but also their compatibility with flexible substrates. The PVAc gives dielectric constant values in the range of 3.2–8.3, which can be adopted as a good gate insulator for OTFTs. The fabricating condition of OTFTs using the PVAc was improved by both adjusting its viscosity with that of a medium, and controlling the surface morphology and spin coating conditions. All these meet the requirement for a new organic gate-insulator, which can improve the performance of the present OTFTs.