In this experiments, male of the ICR strain were used and were injected intraperitoneally with different dose of ,125,I. The rate of chromosomal abnormalities in mouse germ cells, and its changes with time were studied. The results showed that: (1) From 1 to 28 days after injection of 555 kBq of ,125,I, the rate of chromosomal abnormalities of germ cells reached a peak at 1 day. During that time, the abnormal rate in spermatogonias is 1.8%, which is equal to that in spermatocytes. After that, the abnormal percentages in those cells were quickly droped down. (2) The rates of chromosomal aberrations in spermatogonias in males treated with 0, 175, 555 and 1665 kBq of ,125,I at 1 day after injection were 0.14%, 0.45%, 1.80% and .2.65% respectively. Similarly, the chromosomal abnormal rates in spermatocytes were 0.13%, 0.60%, 1.80% and 2.20% accordingly. These results indicate ,125,I can induce a significant increase in the percentage of chromosomal aberrations of germ cells in male treated with ,125,I. The results also provide further evidence of the cytogenetic effects to mammalian germ cells of ,125,I.