Nanotechnology has become increasingly internalized into pharmaceuticals & cosmetics and is of great significance as an approach to killing or reducing the activity of numerous microorganisms. Natural antibacterial materials, such as zinc and silver, are being claimed to possess good antibacterial properties. Nano-sized particles of ZnO have been claimed to have pronounced antimicrobial activities than large particles. Antimicrobial/antifungal potential of ZnO on five pathogens (Escherichia coli MTCC 443, Staphylococcus aureus MTCC 3160, Bacillus subtilis MTCC 441, Aspergillus niger MTCC 281, Candida albicans MTCC 227) and the influence of particles size of these inorganic powder on its antimicrobial /antifungal efficacy was considered in the present study. Results indicated that zinc oxide nanoparticles do have strong antibacterial and good antifungal activity against selected strains of bacteria and fungus as compared to that of conventional zinc oxide particles.