In this work, magnesium oxide micro/nano particles were prepared using laser ablation in deionized water. This is technique very simple, cheap and a single step method. In the present work, at which ablation of pure Mg metal target in deionized water was accomplished using 9nsec Q-switched Nd:YAG laser at 1064 nm laser wavelength, the effect of laser energy on particle size material and the effect of number of laser pulses on optical properties and surface morphology have been studied. UV-visible measurement showed that a red shift in the absorption spectra of MgO NPs is obtained with increasing number of laser pulses. X-ray Florence's (XRF) investigation showed the Mg metal powder percentage purities. Particle size analysis (PZA) investigation showed the particle size distribution of magnesium in deionized water after laser ablation. Atomic force microscope (AFM) investigation showed that magnesium oxide nanoparticles have root mean square of surface roughness 0.954 nm and particle size distribution of magnesium was (15-155)nm after laser ablation.