Different concentrations of Mg-doped ZnO nanoparticles (NPs) were synthesized by coprecipitation technique at 60°C. XRD data are used to study phase purity and crystal structure in different doping concentrations. The results indicated that increasing the doping from 0~7.5 wt.% caused a subsequent increase in FWHM in XRD and an associated systematic shift towards higher wavelength in the optical properties. Finally, the sensing of UV light is tested by observing the response of nanoparticles by exposing them to UV light and measuring the resistance in presence and absence of UV light.