We investigated influence of the self-diffraction effect on optical Kerr signals of Bi2O3-B2O3-SiO2 glass (BI glass) and CS2 in femtosecond non-collinear pump-probe optical Kerr experiments. By measuring the dependence of the Kerr signals on the pump power and on the polarization angle between pump and probe beams, we found that the optical Kerr signals of CS2 consisted of two components: a fast response and a slow response,which were attributed to the self-diffraction effect and the photoinduced birefringence effect, respectively. The contribution of the self-diffraction effect to the Kerr signals increased with increase of the pump power. For the BI glass, no evident influence of self-diffraction on the Kerr signals was observed.