Abstract: The immature germ cells of human semen were used for study of the relation between chromosomal damage and male infertility.Semen samples are collected from 31 infertile men and 5 fertile donors.The results show that the micronucleus (MN) frequency of 9 cases are statistically higher than that of control group.The highest MN frequency is 122‰ and the lowest is 16‰ in 20 cases.In other 11 cases which are azoospermia or polyspermia,we have not observed the MN for lack of immature germ cell in the semen.The high MN frequency invariably accompanied the non-disjunction of meiosis and high frequency of diploid and tetraploid spermatids or sperm.Our results also indicate that the increase of micronuclei is a possible factor of male infertility.The use of MN as an indicator of genotoxic exposure of man is also discussed.