In this research the effect of X-ray with two different energies (6&10) MeV on the number of T-cells in whole blood samples collected from 50 donors (only men) was studied. Blood samples were exposed to (0,5,10,15,20,25,30,35,40) Gray doses of X-rays. The absolute lymphocytes number (Lym), T-cell % and T-cell number) were measured before and after irradiation, then the reduction of each value was calculated. By making comparison between the effects of two energies, it was observed that the use of X-rays 6MeV is more useful because T-cell number reduced with increasing the doses more than when using X-ray 10Mev.