Hydroxyapatite (HA)/titania composite coatings were deposited on titanium alloy substrates using the high velocity oxy-fuel (HVOF) technique. Chemical reactions between the mechanically blended HA and titania particles in the HVOF stream were analyzed. Qualitative phase analysis through X-ray diffraction (XRD) on the composite coatings showed that the chemical reaction between titania and HA occurred during the impingement stage. High temperature differential scanning calorimeter (DSC) analysis revealed that the reaction temperature was 1410 C. The activation energy of the chemical reaction between HA and titania demonstrated a value of 5441.46 kJ/mol obtained through the multiple-heating-rate method. Chemical bonding caused by the reaction between the components was suggested, which may be mainly responsible for the trapping of titania particles during the impingement. Transmission electron microscope (TEM) observation identified the reaction zone and phase distribution area within the HA/titania composite coatings. It demonstrated that the reaction products located around titania were beneficial for the improvement of coating structure. Furthermore, in vitro bioactivity of the HA/titania composite coatings in simulated body fluid (SBF) was revealed. Results showed that the coatings were fully covered by a bone-like apatite layer after 7 days’ incubation.