Background: WHEY protein is a high-quality protein source that is easily absorbed and utilized by the body. It has a beneficial effect on pregnancy and neonatal outcomes. Aim: To evaluate the impact of WHEY protein on pregnancy-neonatal outcomes and its prophylactic effect on Fetal growth restriction (FGR) cases. Patients and methods: This study was a prospective randomized, controlled clinical trial conducted on 300 pregnant females from attendees of obstetrics and gynecology clinics of Al Azhar University Hospitals. They were randomly divided into two groups: Case group: The intervention group (150 cases) received a daily WHEY protein supplement containing 25 grams of protein, and the Control Group: 150 cases received a placebo supplement. Results: There was no statistically significant difference between the studied groups regarding demographic criteria (P>0.01), and the prevalence of FGR was (20% vs 18.75) in the studied groups. According to fetal biometry at birth, there was no statistically significant difference regarding sonographic parameters between the appropriate gestational age (AGA) in the studied groups (P>0.01). There was no statistically significant difference between the two groups regarding complete blood parameters, platelets, or PTT (P>0.01). There was a highly statistically significant difference regarding PT between the studied groups (P<0.001). There was no statistically significant difference between the two groups regarding liver and kidney function tests (P>0.01). There was a highly statistically significant difference regarding total proteins and serum calcium between the studied groups (P<0.001). Conclusion: WHEY protein supplementation did not affect fetal growth, but it improved some maternal parameters, such as total protein and PT.