Nano scale NiO and Cr doped NiO nanoparticles (NPs) have been prepared by simple chemical co-precipitation method. The structure, morphology, band gap energy and magnetic properties of the synthesized samples have been examined by X-ray diffraction, SEM, HRTEM, UV absorption and VSM, respectively. The insertion of Cr ions into NiO NPs gives significant changes in structural and magnetic properties. The crystalline size of Cr-doped NiO was calculated and it is around 20 nm. The UV absorption study shows strong absorption peak around 300 nm. The magnetic property was studied using Vibrating Sample Magnetometer (VSM) and NiO NPs exhibit super paramagnetic behavior, which differs from bulk form whereas Cr-doped NiO NPs magnitization curve recorded the appearance of diamagnetic behaviour and was found suitable for spin value applications.