Radioprotective effcts of pre-treated GS on germ cells in mice were observed in this study. The results were shown as follows: (1) Various concentrations of GS (12.5—200 mg/kg) have obvious protective effects on primary spermatocyte chromosome aberrations induced by 3.0 Gy X-ray,the most effectively protective dose being 50 mg/kg. (2) 50 mg/kg GS has protective effect on chromosome translocations in spermatogonial stemcells exposed to various X-rays doses (1.0—9.0 Gy). (3) GS may prevent reduction of sperms as well as decrease markedly UDS induced by X-rays. According to the experimental results, it was preliminaryly suggested that the preventive mechanism of GS might be associated with anti-free redical effect of ginsen, thereby reducing DNA or chromosome damage, but it was still required further study.