Abstract： Objective To study the effect of maternal deca-brominated diphenyl ether (PBDE-209) exposure on the microstructure and calmodulin-dependent protein kinase Ⅱ (CaMK Ⅱ) content in the hippocampus of the offspring rats. Methods Three-month-old female Wistar rats were exposed to peanut oil suspensions of commercial BDE-209 administered by daily oral garage at the doses of 100, 300, 600 and 1200 mg/kg (groups A, B, C, and D, respectively). The control rats (group E) were given only peanut oil of the same volume. The microstructure of the hippocampus of 5 offspring rats from each group was observed microscopically using HE staining. Ten offspring rats from each group were examined for CaMK Ⅱ content in hippocampus using enzyme-linked immunosorbent assay. Results Obvious histomorphological changes were found in the hippocampus of the offspring rats in groups C and D. The CaMK Ⅱ content in the hippocampus decreased with the increase of the doses of BDE-209 exposure, and compared with group E, the offspring rats in groups C and D showed significantly decreased CaMK Ⅱ content in the hipposcampus (P<0.05, respectively), but those in groups A and B showed no significant variations in CaMK Ⅱ content (P>0.05, respectively). Among the experimental groups, compared with group D, the offspring rats in group A showed significant decreased in CaMK Ⅱ (P<0.05), but those in group B and C showed no significant variations (P>0.05). Conclusion Maternal BDE-209 exposure can induce histological changes in the hippocampus, decrease the neuronal number, and lower CaMK Ⅱ content in the hippoeampus of the offspring rats to affect the development of the nervous system.