The hydrogen storage properties of Ti1.2Fe+xwt%Mg(x=1,3,5) alloys have been investigated. The results show that the modified alloys can be activated at room temperature without any thermal treatment because of the addition of Mg and excess stoichiomentriy of Ti in alloys. The alloy Ti1.2Fe+3wt%Mg(Ti1.2FeMg0.12)is comparatively light in weight and has a large storage capacity,attaining 1.9wt%H2(213 ml/g),and small pressure hysteresis, so suitable for the hydrogen storage system with portable hydrogen fuel cell power. In the paper, the influence and mechanism of the addition of Mg and excessive Ti on the activation behavior and hydrogen storage capacity for the alloys have also been discussed.