Synthesis of MgO nanoparticles through Chemical precipitation method by varying calcination temperatures. The temperature effects on the surface morphology, size of nanoparticles have been reported. The synthesized samples were characterized by various analytical techniques such as X-Ray diffraction (XRD), Scanning Electron Microscope (SEM), Energy dispersive X-ray analysis (EDX) and Fourier transform infrared spectroscopy (FTIR). XRD and SEM exhibits the increase of crystallinity with sharp intense peak and increase of size with varying morphologies respectively with respect to the increase of calcinations temperature. The elements presented in the sample were found by EDX. FTIR analysis confirmed the presence of functional groups in MgO nanoparticles. Antibacterial studies were done on gram positive (S.Aureus), (Pseudomonas) and gram negative (E.coli) bacteria by agar well diffusion method. It is found to be the zone of inhibition decreases with with increasing calcinating temperature.