Zinc Oxide (ZnO) nanoparticles are used in the field of nanomedicine. ZnO is non-toxic and compatible with biological system. The major problem of wound is infections. The infections delays wound healing. Usage of Nanomaterials like ZnO nanoparticles for wound healing is promising. ZnO nanoparticles are synthesised by wet chemical method. It is annealed at 300, 500, 700, and 900 degrees C for 3 h. ZnO nanoparticle morphology and size distribution are analysed by XRD, FTIR and TEM. The influences of particle size on fibroblast cell growth (NIH3T3) and on antimicrobial activity are analysed. The growth of fibroblast cell is higher with ZnO nanoparticles of larger particle size. Further the MTT analysis, fluorescence calcein AM cell staining and F-actin analysis confirms the growth of fibroblast cells with improved biocompatibility behaviour. The antimicrobial activity is higher for ZnO nanoparticles of lower particle size. Confocal microscope analysis and Zone of inhibition analysis confirms the antimicrobial activity of ZnO nanoparticles.