Poly(3-[2-(5-hexyl-2-thienyl) ethenyl]-2,2'-bithiophene) (P2, see Scheme 1) with conjugated thienylvinyl side chain was synthesized by copolymerization of the thiophene units with and without conjugated side chain with Pd-catalyzed Stille coupling method. For comparison, P1 with the hexyl side chain instead of conjugated side chain was also synthesized. P2 film shows broad absorption in the visible region with absorption edge at about 700 nm. The solution-processed polymer field-effect transistors were fabricated and characterized with bottom gate/top contact geometry. The organic field-effect transistors (OFET) based on P2 showed an average hole mobility of about 0.034 cm(2)/Vs (the highest value reached 0.061 cm(2)/Vs) upon annealing at about 180 degrees C for 30 min, with a threshold voltage of -1.15 V and an on/off ratio of 10(4) with n-octadecyltrichlorosilane (OTS) modified SiO2 substrate. In comparison, the OFET based on P1 displayed a hole mobility of 8.9 x 10(-4) cm(2)/Vs and an on/off ratio of 10(4) with OTS modified SiO2 substrate. The results indicate that the polythiophene derivative with conjugated thienylvinyl side chain is a promising polymer for the application in polymer field-effect transistors. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5304-5312, 2009