To study the internal radiation effects of tritiated water on the amount of cells of peripheral white blood cell (WBC) and micronucleus rate of polychromatic erythrocytes (MNPCE) in mice, C57BL/6J mice were randomly divided into several groups: one control group, two groups with injection of different initial concentration of T,2,O, and five groups with injection of same initial concentration of T,2,O, but different time for sacrifice (i.e. the 2nd, 4th, 6th, 10th and 28th day after injection). The amount of peripheral WBC and MNPCE were measured. In different initial concentration groups, the MNPCE in bone marrow increases (,p,<,0.05) with increment of cumulative doses. The amount of peripheral WBC of the group with initial concentration of 16.65×10,5,Bq/g is higher than that of the other groups. In the same initial concentration groups, the total number of peripheral WBC decreases (,p,<,0.05) before the 6th day and recovers at the 10th day after injection. The MNPCE increases continuously to the 28th day after injection. The amount of peripheral WBC and the MNPCE in bone marrow can be used as early sensitive indicators for internal exposure to tritium irradiation.