Abstract: Objective To define the neural tube defects teratogenicity effects of cyclophosphamide and its mechanism on rats,provide basis for further study on prevention and cure.Methods The pregnant rats were randomly divided into control and four experimental groups according to their bodyweight,The cyclophosphamide intakes among five groups were 7.5,10.5,12.5,15.0mg/kg via intraperitoneal administration on the 13th day of gestation.On the 14th day of gestation,three rats were randomly killed and embryos were checked through optical microscopy;the other rats were killed on the 20th day of gestation,the biochemistry index and pathology slice were examined,the skeleton examples were made.Results The frequency of abnor malt y,skull defects of embory and MDA、NO in serum of pregnant rats had sig nificantly positive correlation with the intake of cyclo phosphamide;while SOD and developmental index had significantly negative correlation.The group of 12.5mg/kg had a high frequence of neural tube defects and a low frequence of death,the results from optical microsco pyindicated some typical changes of apo ptosis.Conclusion To make a model of neural tube defects,the intake of 12.5mg/kg was feasible;oxidation and neurons apoptosis might be involved in its teratogenesis.