Abstract Thermal decomposition of the FeTi 1.13 hydride was investigated after hydrogen absorption-desorption cycling at 50 °C in impure hydrogen containing 680 ppm oxygen. The number of cycles exerted a remarkable effect on the variation in the rate of hydrogen desorption and in the pressure increase with temperature. The alloy after a small number of cycles exhibited only a single desorption peak whereas amplifying and splitting of the desorption peak was observed in curves after a large number of cycles. Whilst the amount of hydrogen absorbed by the alloy decreased on each cycle, decomposition of the metal hydride became more and more difficult at 50 °C, and the thermal decomposition of the metal hydride produced a larger amount of hydrogen with an increase in the number of hydrogen absorption-desorption cycles. This was attributed to the fact that hydrogen desorption is never completed but some of the absorbed hydrogen is retained on each cycle. It is concluded that the formation and growth of titanium oxide “TiO” plays an important role in the accumulation of hydrogen on each cycle; this causes a unique thermal decomposition of the metal hydride which is different from that after cycling in pure hydrogen or CO-contaminated or CO 2-contaminated hydrogen.