Abstract: A series of Mg_xNi_1-xO alloy films were prepared by pulsed laser deposition.In the procedure, the laser energy density was fixed at 5 J/cm², while the temperature of heated substrate varied from 300 ℃ to 700 ℃.The composition and microstructure of the as deposited films were characterized by atomic force microscopy(AFM), transmission electron microscopy(TEM) and X -ray photoelectron spectroscopy(XPS). The influence of annealing on the sample was also studied. UV-VIS spectrophotometer was used to analyse the transmittance of the films. Some interesting results were obtained. The as deposited Mg_xNi_1-xO film was found constituted by crystalline component and amorphous one. The ultraviolet absorption edge were located at about 290 nm, near the superior limit of solar-blind wavelength. It is also found that the film prepared at 5 J/cm²-500 ℃ have strong absorption within short wave range, but scarce absorption in infrared and visible wave band, which is useful to ultraviolet detection.The annealing treatment was very effective to improve the surface quality of the film, but had little effect on the optical band gap.