Abstarct: In this study NiO/PMMA composite was prepared in three step. Step in the first, nickel oxide nanoparticles synthesized by chemical precipitation via reaction between NiCL2.6H2O and calcined at 300℃for 2 h. to improve their dispersibility in an organi media, NiO nanoparticles were prepared by treating with oleick acid in ethanol. then, modified NiO nanoparticles was dispersed in methyl methacrylate monomer and in situ emulsion polymerization was carried out. Nanoparticles and nanocomposites were characterized by XRD, FT-IR, SEM. Thermal stability of the nanocomposite were investigated by TGA and DSC.finally, Nanoparticles and Nanocomposite photocatalyst activity were investigeted the photo deagradation of methyl orange by UV and calculated their PDP. modified nanoparticles and nanocomposite photocatalyst activity were minor than NiO nanoparticles.