We have examined the nonlinear optical properties of a main chain organic polymer waveguide in the 1.5 &mgr;m wavelength region. The nonlinear absorption coefficient was estimated to be &agr;2=0.8–2×10−11m/W in the 1.48–1.61 &mgr;m wavelength range. The wavelength dependence of the nonlinear absorption coefficient suggests that the strong nonlinear absorption originates from two step absorption through overtones of C–H vibrational absorption. The nonlinear refractive index was estimated to ben2=2.8(±0.3)×10−18 m2/W at a wavelength of 1.55 &mgr;m. The nonlinear absorption would restrict the applicability of the waveguide to all‐optical switching in this wavelength region. ©1995 American Institute of Physics.