This paper reports on SHI induced modifications in the structural and optical properties of ZnO/PMMA nanocomposites. The ZnO nanoparticles of different sizes were synthesized by chemical route using 2- mercaptoethanol as capping agent. These ZnO nanoparticles were dispersed in the PMMA matrix to form ZnO/PMMA nanocomposites which were confirmed by X-ray diffractometer studies. These ZnO/PMMA nanocomposites were then irradiated by swift heavy ion irradiation (Ni⁺⁸ ion beam, 100 MeV) at a fluence of 1 x 10¹¹ ions/cm².  Absorption and Photoluminescence spectroscopy revealed a red shift in the band gap and enhanced green luminescence about 526 nm after irradiation with respect to the pristine ZnO/PMMA nanocomposites respectively.