Third‐order nonlinear optical properties of As2S3‐based glass fibers are studied at a wavelength of around 1.55 &mgr;m. Through time‐resolved pump‐probe measurements and analysis of spectrum broadening due to self phase modulation, it is confirmed that As2S3‐based glass fibers are capable of instantaneous nonlinear refractive response to a subpicosecond pulse. Stimulated Raman scattering (SRS) with a Stokes shift &Dgr;k=344 cm−1is observed using a picosecond pump pulse. The Raman gain coefficient was estimated to be 4.4×10−12(m/W), which is two orders of magnitude higher than that for silica fiber. The relaxation time of the Raman contribution to nonlinear refraction is estimated to be 97 fs and the influence of the SRS on subpicosecond pulse propagation is observed as a low‐frequency Raman gain. The two‐photon absorption (TPA) coefficient is estimated to be &agr;2=6.2×10−15(m/W) through a transmission change measurement. The TPA figure of merit for As2S3glass at a wavelength of 1.55 &mgr;m is estimated to be low enough for all‐optical switching applications. ©1995 American Institute of Physics.