In order to develop low-cost ZnO nanodevices with high performance an d simple structure,in this paper,ZnO nanocrystalline thin films were prepared on p-type silicon (p-Si) s ubstrates by thermal decomposition method.The morphology,crystalline structure a nd optical properties of ZnO nanocrystalline thin films were investigated by field emission scanning electron microscopy (FESEM),X-ray diffractometer (XRD),ultraviolet-visible (UV-Vis) spectrophotometer and the f luorescence spectroscopy, respectively.The results show that the irregular particle-like ZnO nanocryst als with a polycrystalline hexagonal wurtzite structure are formed on the p-Si substrate.The optical transmittance of ZnO nanocrystalline thin films in the visible region is above 90%,its optical bandgap is 3.26eV,and only a stro ng near band edge (NBE) emission peak is found at 387nm.Moreover,it is found that the ZnO nanocrysta lline thin film/p-Si heterojunction exhibits rectifying behavior in the dark and under 365nm UV ill umination,indicating the formation of a diode.In the dark,the rectification ratio,turn-on voltage,id eal factor and reverse-bias saturation current of this diode are 3.95(±2.46V),0.7V,4.65and 4.57×10－8 A,res pectively.Under 365nm UV illumination, its rectification ratio is increased sharply to 24.85(±0.65V),suggesting that this diode has a high response to 365nm UV illumination,and it is suitable to be applied as UV photodetectors.