The swelling behavior of 20% cold-worked 15-15Ti steels with (0.23-0.40) wt% titanium and (0.42-0.81) wt% silicon content after heavy-ion beam irradiation has been investigated by transmission electron microscopy. The results show that 15-15Ti steel with higher titanium content displays lower swelling. As silicon content increases, the cavity size and the swelling of the 15-15Ti steels decrease obviously. Titanium and silicon may play important roles in suppressing the cavity nucleation and growth in 15-15Ti steel.