Abstract W is a candidate for plasma facing material and oxide layers are highly anticipated on W surface. We have studied deuterium (D) retention in tungsten oxide (WO 3) films and thermal release of deuterium. WO 3 films, prepared by oxidation of W metal sheet, were exposed to D 2 plasma under AC glow discharge at the applied voltage V up to a few kV and DC discharge. D-retention in W has been studied for comparison. The amount of D retained in the WO 3 films and W were analyzed by detecting α particles from the nuclear reaction, D( 3He, α)p, using 0.7 MeV 3He + ions. We find that D-uptake in WO 3 film is much larger than in W. According to thermal desorption, release of D 2 occurs at ∼180 and 450 °C.