Abstract: The characteristics of absorbing H₂-D₂ mixture in titanium was researched and the separation factor of hydrogen isotopes was measured. It is found that there is a linear relation between the separation factor’s logarithm and absolute temperature’s reciprocal as ln α＝-0.13+107/T in the temperature range of 100~300 ℃. The separation factors of titanium absorbing mixed gas with various composition at 200 ℃ are independent of the composition of mixed gas, and there is an obvious isotope effect for the absorption of H₂-D₂mixed gas in titanium and it is easier to absorb protium in titanium.