As UV irradiation on titania causes several effects, such as decomposing organic substances and attaining super-hydrophilic surfaces. the present study explored the UV irradiation effects on apatite deposition on titania gel films (anatase) that were developed on a few substrates: pure titanium (Ti), stainless-steel (SUS316L), alumina (Al(2)O(3)) and glass slide (GS). Those substrates were dip-coated with a precursor sot (Ti(OC(2)H(5))(4) : C(2)H(5)OH : H(2)O : HNO(3) = 1 : 50 : 2 : 0.2) and heated at 500 degrees C for 10 min before irradiated with UV light (365 nm, 170 mW/cm(2)) in air for 1 h. They were subsequently soaked in simulated body fluid (SBF. Kokubo solution) and their in vitro apatite formation was evaluated by X-ray diffractometry and scanning electron micrograph. It was found that the UV irradiation enhanced apatite formation on the titania gel film on Ti and SUS by shortening the induction time. However, least effects were found for the titania gel films on Al(2)O(3) and GS as they did not deposit apatite within 7 days, even with the UV irradiation. These results indicated that UV irradiation had limited effects to enhance in vitro apatite formation on the titania films, i.e., it depended on the substrates.