RF sputtering process was applied to produce thin hydroxyapatite(HAp, Ca10(PO4)6(OH)2) films on Ti-6Al-4V alloy substrates. The effects of different heat treatment conditions on the bonding strength between HAp thin films and Ti-6Al-4V alloy substrates were studied. Before deposition, the Ti-6Al-4V alloy substrates were heat treated for 1hr at 850°C under 3.0×10-3torr, and after deposition, the HAp thin films were heat treated for 1hr at 400°C, 600°C and 800°C under the atmosphere, and analyzed optical microscope, FESEM, FTIR, XRD, nano-indentor, micro-vickers hardness, respectively. Experimental results represented that the HAp thin films on the heat treated substrates had higher hardness than none-heat treated substrates before the deposition.