Hydroxyapatite [Ca10(PO4)6(OH)2, HAp] is the major constituents of bones and hard tissues in mammals. In the last few years, HAp nanoparticles have been used as an ideal tool for the transformation of human hard tissues due to their high biocompatibility and easy biodegradability. Currently, metals are widely used in orthopedics to increase the bioactivity of hydroxyapatite. Among these metals, zinc is an essential trace element present in human bones and teeth. It plays important roles in increasing osteoblast adhesion and alkaline phosphatase activity of bone cells. In the present study, different amounts of pure and ZnO (0% – 43%) doped nano Hydroxyapatite powders were synthesized by the sol-gel method. The properties of pure and Zn doped nHAp powders were characterized using X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Energy dispersive X-ray analysis (EDAX). The results of X-ray diffraction studies revealed the progressive increase in the average crystallite size from 49 to 100 nm with increasing ZnO concentration found to be 49–100 nm. The in vitro antimicrobial activities of the synthesized pure and Zn-doped nHAp powders were investigated against gram-negative bacterial strains using the disc diffusion method. The antimicrobial activities of pure and doped nHAp samples were observed irrespective of the ZnO content.