Objective: To investigate the effect of aspirin on fetal weight in fetuses with idiopathic asymmetrical intrauterine growth restriction (IUGR) complicated by abnormal umbilical artery Doppler indices. Materials and methods: The study was a randomized controlled trial conducted at Woman’s Health Hospital, Assiut, Egypt, between June 2016 and the January 2017 included 60 pregnant women (28_30 weeks) with idiopathic asymmetrical IUGR associated with abnormal umbilical artery Doppler indices. Women were randomly assigned to group I (aspirin 75 mg) daily for four weeks or group II (no intervention). The primary outcome was the fetal weight after four weeks. Secondary outcomes included Doppler blood flow changes in the umbilical artery plus delivery and neonatal outcomes. Results: The estimated fetal weight and umbilical artery blood flow increased significantly in aspirin group (p¼.00) when compared with no intervention group. As regard neonatal outcomes; aspirin group showed better results and encouraging outcomes (p<.05). Conclusions: Aspirin improves fetal weight and umbilical artery blood flow in idiopathic asymmetrical IUGR fetuses complicated by abnormal umbilical artery Doppler blood flow.