Objective To investigate the MRI features of normal uterus and fetal development during late stage of pregnancy in rhesus monkeys.Methods Magnetic resonance imaging(MRI) at 1.5 Tesla was performed in 3 adult female rhesus and 3 rhesus at 135 days of pregnancy.The MRI signal intensity and anatomic structure of normal uterus and characteristics of fetuses were retrospectively evaluated.Results On coronal T_1weighted images,the normal uterus wall showed moderate signal intensity with a elliptic shape.While on sagital view,the uteri appeared a cucurbit shape on T_2 weighted images(T2WI),and three layers of the structure of uterus wall depicting different signals were noticed.On sagital section(T2WI),the signal intensity of muscular wall of uterus body was slightly higher than that of cervix,the signal transition zone was at the junction zone of the uterine body and cervix.During late stage of pregnancy,the uteri were enlarged markedly but the uterus wall was substantially thinned.The placenta,brain,spinal cord,liver and lung of the fetus were well demonstrated.Conclusion MRI imaging can well demonstrate the shape,size and wall layers of uterus and anatomic structures of the fetus.It is a noninvasive approach for evaluating the female genital organ changes and may be helpful in detection of possible abnormal development of fetus in humans.