Herein,we reported the nonlinear optical response of triiodide (CH3NH3PbI3) and mixed halide (CH3NH3PbI3-xClx) perovskite thin films.The results demonstrated that they have large nonlinear refractive index (NRI),three orders of magnitude larger than that of silicon.Particularly,the NRI of CH3NH3PbI3-xClx is more than two times larger in comparison to that of CH3NH3PbI3.Likewise,both of them have been proven to possess saturable absorption effects with small nonlinear absorption coefficients which indicate that they can maintain excellent absorption under high-intensity irradiation and are favorable to modulators towards large-energy pulsed laser.Considering the saturable absorption effect,we demonstrated a pulsed laser with the perovskite as a pulse modulator.These results above indicate the potential for perovskites to be employed in nonlinear optoelectronic devices.