Zinc substituted nano hydroxyapatite (n-ZnHA) has been synthesized by sol-gel technique. Calcium nitrate tetrahydrate, Zinc nitrate and potassium dihydrogen phosphate were used as precursors under water based solution. Triethanolamine (TEA) was used as a capping agent. The synthesized nanopowder was calcined by conventional means at three different temperatures 800 C, 1000 C and 1200 C for 3hrs. The n-ZnHA powders were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and thermal gravimetric analyser (TGA) techniques. The results showed that Zn substitution has exhibited an evident inhibitory role on synthesis of HA through a reduction in crystallite size and a decrease in thermal stability. Bioactivity behaviour of n-ZnHA was assessed through in-vitro study in simulated body fluid (SBF) and n-ZnHA is found to be more bioactive as compared to nano hydroxyapatite synthesized without Zn substitution.