The optical limiting characteristic of semiconductor nano-particles Bi2S3 and NiS were investigated in experiment. Their nonlinear limiting thresholds are 0.11 J/cm2 and 0.21 J/cm2, respectively. From the result of the open Z-scan for the samples, the nonlinear absorption coefficients of Bi2S3 and NiS are β≈8 cm/GW and β≈9 cm/GW, respectively. It was found that the measured result of the closed scan of NiS in alcohol solution indicates the self-focusing effect in it. That is, the nonlinear refractive index of NiS solution n2>0, corresponding γ≈2.66×10-41 cm2/GW.