In order to improve the efficiency of polymer photodiodes,ZnO thin film was introduced into the polymer photodiode.Two types of devices were made,ITO/MEH-PPV/Al and ITO/ZnO/MEH-PPV/Al.The thickness of ZnO film was changed in the range of 3 nm and 6 nm.The photoconductivity of these devices was measured.We found that the photocurrent of the device without ZnO is smaller than that one with ZnO,and it increases with the increase of the thickness of ZnO.We compared the absorption spectra of ZnO and that of MEH-PPV,and found that the absorption peak of MEH-PPV was consistent with the peak of the photocurrent-wavelength curve.The results suggest that the carriers were produced in the MEH-PPV and the ZnO film facilitates the dissociation of the exciton and enhances the transportation of the carriers.