A study of deuterium conductivity and diffusion in the oxide perovskite La0.9Sr0.1YO3-delta is presented in this work. Deuterium ions were implanted into La0.9Sr0.1YO3-delta (50 keV, 1 x 10(16) atoms/cm(2)) and the corresponding deuterium depth profile was determined by SIMS and compared with a Monte Carlo simulation (TRIM96). This implant was used as a standard for the determination of deuterium concentration in a La0.9Sr0.1YO3-delta sample pre-treated in D2O atmosphere. In this way, it was fully confirmed that La0.9Sr0.1YO3-delta incorporates water at high temperatures. The conductivity of La0.9Sr0.1YO3-delta was measured in D2O atmosphere and compared with other proton (deuteron) conductors. Concentration and conductivity data were used in conjunction to estimate the deuterium diffusivity and the constant of reaction of (heavy) water incorporation into LaYO3. Some comments on the catalytic activity of this oxide are made.