We have reported the conjugation-length dependency of unsubstituted oligo-p-phenylenevinylenes (OPVs) on the performance of organic field-effect transistors (OFETs). The experimental results have shown that the appropriate conjugation-length exists for obtaining high-performance OFET's with OPVs evaporated on the substrate at room temperature. It is considered that observed mobilities are determined by the hole injection barrier and the molecular orientation in the film. On the other hand, high-performance OFET's using OPV with a long conjugated length were obtained when the OPV was evaporated on the substrate at optimum temperatures. The OFET exhibited field-effect hole mobility up to 1.5 x 10(-1) cm(2) V-1 S-1. (c) 2007 Elsevier B.V. All rights reserved.