In this work, improvement of mechanical and electrical properties of gate dielectric layer for flexible organic thin film transistor (OTFT) devices was investigated. In order to increase the mechanical flexibility of PVP (poly(4-vinyl phenol) organic gate dielectric, a very thin inorganic $HfO_2$ layers with the thickness of $5{sim}20nm$ was inserted in between the spin-coated PVP layers. Insertion of the inorganic $HfO_2$ in the laminated organic/inorganic structure of PVP/$HfO_2$/PVP layer led to a dramatic reduction in the leakage current compared to the pure PVP layer. Under repetitive cyclic bending, the leakage current density of the laminated PVP/$HfO_2$/PVP layer with the thickness of 20-nm $HfO_2$ layer was not changed, while that of the single PVP layer was increased significantly. Mechanical flexibility tests of the OTFT devices by cyclic bending with 5 mm bending radius indicated that the leakage current of the laminated PVP/$HfO_2$(20 nm)/PVP gate dielectric in the device structure was also much smaller than that of the single PVP layer.