We report measurements of the third-order nonlinear optical properties of a newly synthesized thiophene-based copolymer. The nonlinear transmission measurements were performed on the copolymer dissolved in tetrahydrofuran by employing the single beam Z-scan technique. Q-switched laser output at 532-nm wavelength was used for this purpose. The nonlinear absorption coefficient, beta, nonlinear refractive index, n(2), and the real and imaginary parts of third-order susceptibility, chi((3)), were, 18.93 cm/GW, 3.037 x 10(-17) m(2)/w (-1.022 x 10(-10) esu), 1.512 x 10(-20) m(2)/V-2(-1.080 x 10(-12) esu) and 0.399 x 10(-20) m(2)/V-2 (0.285 x 10(-12) esu), respectively. The excited state absorption crosssection sigma(exc), was found to be larger than the ground state absorption crosssection sigma(g), indicating reverse saturable absorption (RSA) in the copolymer sample. The copolymer exhibits an optical power limiting threshold of about 120 mu J and saturated output of less than 80 uJ. Hence, the copolymer seems to be a promising material for photonic device applications. POLYM. ENG. SCI., 49:875-880, 2009. (C) 2008 Society of Plastics Engineers