Abstract: BACKGROUND ＆ AIM: To study the effect of exposure to hydroxylammonium nitrate (HAN)on micronucleus(MN) frequency of polychromatic erythrocytes(PCE) from Wistar rats marrow. METERIAL AND METHODS: Different doses of HAN at 6.97 mg/kg, 13.93 mg/kg, 27.86 mg/kg were administered to the three treated groups by intraperitoneal injection，and the negative control group was treated with 0.9 ％ NaCl. The treatment had been performed every other day for 90 days. After the last treatment in 90 th day, 2/3 of the rats were sacrificed by cervical dislocation, and after 30 days' recovery we sacrificed the rests. The number of micronucleus per 1 000 polychromatic erythrocytes (PCE) from sternum bone marrow was counted and analysed. RESULTS: In the period of exposure to HAN, the MN frequency of bone marrow cells of Wistar rats treated by HAN wasn't significantly different from that of the negative control group, except for the highest dose group. After 30 days'recovery, the MN frequency treated by HAN was not significantly different from that of the control group. CONCLUSION: Our results suggested that HAN can produces certain genotoxicity，which was reversible but didn't have delayed effect.

Key words: hydroxylammonium nitrate, micronucleus, genotoxicity, rat