Background: Nanoscience and nanotechnology have been established recently a new interdisciplinary science and now a days it is one of the most attractive research area in modern material science. Nanotechnology can be defined as the synthesis, characterization, exploration and application of nanosized materials for the development of science. Objective: To Synthesis of MgO nanoparticles using Neem leaves extract & characterization of MgO nanoparticles with its antioxidant and photocatalytic effects. Methodology: A Quasi experimental type of study in the Department of Pharmacology and therapeutics, Rajshahi Medical College, Rajshahi from January 2018 to December 2018. Prior commencement of the study, approval was taken from the institutional Review Board of Rajshahi Medical College. Results: There was no significant difference between Neem extract and Mg (NO3)2. MgO-NPs vs Mg (NO3)2 showed Mean difference = -0.19, 95% CI of difference = 0.3434 to – 0.03662, P value = <0.05. So, there was significant difference between MgO-NPs. and Mg (NO3)2. Conclusion: Synthesis of nanoparticles were confirmed by changes of colour from yellow to yellowish brown, UV-Vis spectroscopy and also by evaluation of its photocatalytic and antioxidant properties. In the photocatalytic study 88% dye degradation of MgO-NPs was found and antioxidant activity of MgO-NPs was also examined using DPPH assay which showed significant (P< 0.0001) antioxidant properties with 80% DPPH scavenging activity at 100mg/ml concentration.