Background: Pregnant women and their doctors continue to worry about the potential health consequences of maternal weight increase. Objective: The aim of the current work was to describe the accurate maternal knowledge of recommended weight gain during pregnancy and assessment of this knowledge effect on actual gestational weight gain. Subjects and Methods: This cross-sectional study included a total of 523 pregnant women receiving antenatal treatment, attending at the Prenatal Outpatient Clinic, Al-Azhar university hospitals, using a self-administered questionnaire.This study was conducted between October 2016 and April 2017. Results: Low rates of acceptable gestational weight growth (27.6%) and low rates of proper understanding of weight increase recommendations during pregnancy (10.3%) characterize our sample cohort (40.4 percent). Accurate awareness of prenatal weight increase guidelines was linked to healthy weight gain. (P=0.007). Mothers' understanding of healthy weight increase did not improve with higher levels of education. (P=0.458). Conclusion: It could be concluded that the findings of this study support the need for improvements in educational efforts about weight gain in pregnancy. The main source of ANC knowledge especially gestational weight gain knowledge is low. The vast majority of pregnant women do not regularly practice exercise before pregnancy.