Objective:To study the capability of defending against sexual assault of mental retarded women.Method:Fifty rape cases of women judged incapable of defending against sexual assault for mental retardation were compared with fifty cases without intelligent impairment by self-developed questionnaire.Result:The two situations were different in age of the perpetrators, motivation of rape, acquaintance with the perpetrator, time and location of the rape, number of times being raped, and victim's reaction during and after rape.Conclusion:Mental retarded women need more protection in prevention of rape.