Abstract: Objective To investigate the toxic effects of arsenic on brain cellular energy metabolism and ultrastructure in rats.Methods Healthy adult SD rats were randomly divided into five groups (control,low-,moderate- and high-dose arsenic and offspring-producing groups)and the rats in experimental groups were exposed to drinking water containing AS2O3.After 6 and 16 weeks,ATP contents of brain cellular mitochondria were determinined in all groups and cellular ultrastructure changes were observed.Results After arsenic exposure,ATP contents (222.90±3.85 nmol/mg·pr for 6 weeks low arsenic exposure,166.12±4.40 for 16 weeks low arsenic exposure)in brain cellular mitochondria decreased compared to that of the control group (238.57±1.31 nmol/mg·pr)and positively correlated with the exposure dose and time.The contents of ATP in the offspring group (28.66± 2.32 nmol/mg·pr) was much lower than that of adult rats (54.25±4.92 nmol/mg·pr) after exposed to high concentration of arsenic for 16 weeks.The ultrastructures of brain cells showed enlarged rough endoplasmic reticulum and swellen mitochondria.In moderate and high arsenic groups,nuclear swelling and decreased number of organelles were found after exposed to arsenic for 16 weeks.In the offspring-producing group,the intranuclear structures became loose and the number of mitochondria organelles decreased obviously,with porous cytoplasm.Conclusion Arsenicalism causes evident damage of cellular energy metabolism and ultrastructure in rat brain.And the fetus rats are severely affected than the adults rats.