Disclosed is a composition for preparing an organic insulator, including an organic silane material, having a vinyl group, an acetylene group or an acryl group as a functional group for participating in a crosslinking reaction, a crosslinking agent, and a solvent for dissolving the above components. The organic insulator of example embodiments may be provided in the form of a solid insulating film, which may increase charge mobility while decreasing the threshold voltage and operating voltage of OTFTs, and which also may generate relatively slight hysteresis.