Biopolymer_CdSe/ZnS core_shell quantum dot hybrid films were prepared using self_assembly technique. Compared with the absorbance spectrum, the photoluminescence excited by laser with λ=395nm has Stokes shift. The third_order nonlinear optical properties of biopolymer_CdSe/ZnS film were studied by Z_scan setup with femtosecond laser at 790nm. It is found that the nonlinear absorptive signal partially originates from Cde/ZnS quantum dots while the nonlinear refractive signal partially originates from biopolymer chitosan. The magnitudes of them are measured to be β＝6.5×10-6cm/W and n2＝1.5×10-10cm2/W, respectively.