Presence of silica in many biocompatible and bioactive materials has been found to improve the bioactivity. Therefore, using sol-gel method, hydroxyapatite-silica omposite nanopowder (at 600°C) and nanostructured hydroxyapatite-silica composite coating on stainless steel 316L (at 550°C) were prepared and characterized. XRD technique was used to approve suitable phases in the powders and coatings obtained. The effect of the silica content on grain size and crystallinity was also evaluated. FTIR technique was used to identify the functional groups in composite powders and coatings. TEM technique was utilized to evaluate the shape and grain size of nanostructured composite powders. SEM technique was used to study the powder morphology, morphology and surface quality of coating and also coating thickness measurment. EDX was used to determine the elemental analysis of powders and distribution of elements in composite coatings. Evaluation of dissolution rate and bioactivity of composite powders and coatings in physiological saline solution carried out for 21 days in a thermodynamically closed system and for 4 days in a thermodynamically open system respectively. In order to identify the content of Ca ion release from composite powders and coatings, AAS was used. Also, SEM was employed to study the variation of morphology. Quality evaluation of bonding strength of coating to substrate carried out based on the ASTM C1624 standard. Finally, using electrochemical polarization potentiodynamic test, corrosion resistance of coated substrates was evaluated.The results indicated that nanostructured composite powder consists of hydroxyapatite crystalline phase and silica amorphous phase. The crystalinity and crystallite size of hydroxyapatite was decreased by increasing the silica content. Powder dissolution experiment in a thermodynamically closed system showed that compare with hydroxyapatite powder in dissolution stage the Ca ion release of composite powder is increased. This would also accelerate the apatite creation in reprecipitation stage. Evaluation of single-phase and composite coatings modified by 2 wt% oxalic acid, showed high quality surface coating, proper bonding to substrate and thickness less than 3.5µm. Evaluation of bonding strength of coatings showed that composite coatings compare with single-phase coatings have better bonding strength. Coating dissolution experiment in a thermodynamically open system showed that due to the presence of silica in composite coatings, the Ca ion release could be controlled. In addition, the coating morphology evaluation after dissolution test indicated morphology chang of precipitated apatites and consequently increasing bioactivity by increasing silica in composite coatings. Results of electrochemical polarization tests showed that increasing the silica in composite coatings lead to improve the corrosion behavior of coated substrate as well as biocompatibility.