Background: Although the increased fetal morbidity and mortality associated with post-term pregnancy has long been appreciated, most authors have studied gestational age as the alone contributing factor. The influence of other factors such as maternal age, parity, maternal smoking, fetal genders, birth weight and past history of post-term has not been adequately evaluated, Additionally, the accuracy of earlier studies is limited by the fact that they predate the widespread use of both ultrasonography for accurate gestational dating and intensive fetal testing to establish fetal wellbeing. Objective: the present study was conducted to evaluate the effects of prolonged exceeding 287 days of menstrual age on the Doppler flow velocity waveforms in the umbilical, middle cerebral and uterine arteries, and its impact on neonatal outcome to determine the best predictor of adverse outcome in post-term. Patients and Methods: The present study included 50 pregnant ladies All patients were submitted to ultrasound for detection of fetal genders, fetal weight and amniotic fluid index (AFI) Also, they were submitted to color Doppler velocimetery of fetoplacental and fetal vessels including middle cerebral pulsitility index MCA PI), umbilical artery pulsitility index UA PI), middle cerebral resistance index MCA RI), umbilical artery resistance index UA RI), uterine artery pulsitility index UtA PI),and uterine artery pulsitility index UtA RI). Results: In the present study, there was no statistical signification with gestational age, fetal heart rate and parity. The primary  gravida  had the highest incidence. There was higher rate of CS which was significant with prolongation of pregnancy, but with no statistically significant difference between adverse and normal outcome Also, the incidence of males was more than females in our population with no significant relation between fetal gender and neonatal outcome. Adverse outcome was associated with lower MCA PI, MCA RI, AFI, Apgar score, and higher UA RI compared to normal outcome with statistically significant difference between them, but there was no statistically significant difference as regard UA PI, UtA PI, UtA RI. Conclusion: The perinatal morbidity and mortality may be increase in post-term pregnancies. However, the all screening tests and Doppler indices may be normal due to mode of delivery, time of delivery, and type of anesthesia during labor. So, during labor, rapid interference should be taken to decrease incidence of adverse neonatal outcome. In post-term pregnancies with adverse outcomes, impedance to flow in umbilical arteries may be increased, while impedance to flow in the fetal middle cerebral arteries may be decreased, but impedance to flow in uterine arteries may be normal