In this study, a sol-gel process is introduced to fabricate the composite film of polystyrene and titania, using titanium tetraisoproxide as a titania precursor. Pentacene-based organic thin-film transistor (OTFTs) with the composite film as a gate insulator operates at a low voltage below -4V and exhibits high performances, such as threshold voltage of -0.9 V, subthreshold slope of 0.2 V/decade, and mobility of 4.7 cm(2)/Vs, which are mainly attributed to a high dielectric property of the fabricated composite insulator. These results demonstrate that sol-gel derived composite insulators are essentially promising for low-voltage OTFTs with high performances.