Abstract: BACKGROUND ＆ AIM ： To study the teratogenicity and mutagenicity of molybdenum in pregnancy rats. MATERIALS AND METHODS： 105 pregnant Wistar rats , 75 for teratogenicity test，30 for micronucleus test, were randomly divided into 5 groups. The rats in experimental groups were treated with 10,20 and 40 mg/kg molybdenum acid ammonium salts, in negative control group received normal saline and in positive group was given 20 mg/ kg cyclophosphamide . Teratogenicity test was scheduled at day 20 of the pregnancy，and micronucleus test at day 14. RESULTS： Compared with negative control group，the increased weight of the pregnant rats , the percentage of live fetuses, the embryonic body weight in 40 mg/kg and positive control groups were decreased(P<0.01) . The micronucleus rate of marrow cells in pregnant rats, the liver blood cells and peripheral blood cells in the fetus, the rate of skeletal and visceral deformities and in 40 mg/ kg and positive control groups were increased (P<0.01) . The embryonic body and tail length in 40 mg/kg and positive control groups were decreased (P<0.05). The rate of external deformity in 40 mg/kg and positive control groups were increased(P<0.05). Percentage of live fetuses in 20 mg/kg group was decreased (P<0.05) . The micronucleus rate of the liver blood cells and peripheral blood cells in the fetus, the rate of skeletal and external deformityies in 20 mg/kg group were increased (P<0.05). The rate of external deformity in 10 mg/kg group was increased (P<0.05). CONCLUSION：There were teratogenicity and mutagenicity on the rat embryo treated with 20 mg/kg to 40 mg/kg molybdenum acid ammoniumsalts.

Key words: molybdenum, embryonic, micronucleues, teratogenicity, mutagenesis