Abstract: Objective To investigate the influences of γ-ray ir radiation in utero on the rat offspring.s br ain development.Methods Pregnant female rats were exposed to the gamma ray with a signal dose of 1.0G yin utero on Day 17 of gestation.The brain weight and the content of brain DNA and protein were measured at Day 1,4,7,14 and 21 after birth.Results Compared with the control group,the irradiated offspring on day 1,4,7,14 and 21 after birth had a significant reduction in brain weight,brainweight/body weight ratios and content of brain protein.There was a high level of brain DNA on the first day,and a low level on day 4 after birth.Then the levels of brain DNA increased from day 4 to 21 after birth.The level of brain DNA in the irradiated group at day 1 and day 21 decreased significantly compared with the control.Conclusion 1.0Gy γ-ray irradiation of rat embryos(17days)in utero could influence the brain development,which presented the decrease of the brain weight,DNA and protein content of brain.