Ultrafast third-order nonlinear optical responses of GeS2–In2S3–CsI chalcohalide glasses have been measured by using the femtosecond time-resolved optical Kerr effect (OKE) technique at a wavelength of 820 nm. The third-order nonlinear susceptibility was estimated to be as large as 5.12×10−13 esu. The full width at half maximum of the Kerr signal was 120 fs and its response was dominantly assigned to the ultrafast distortion of the electron cloud. The relationship between the structural units and the third-order nonlinear optical responses was analysed by Raman spectra. It is suggested that the covalent bonds of S–Ge or S–In constituting the tetrahedral units [GeS4/2] or [InS4−xIx], respectively, play an important role in the ultrafast third-order nonlinear optical responses of these chalcohalide glasses.