Background: Obesity has been recognized by the World Health Organization as a pandemic nutritional disorder. Egypt has the highest levels of overweight and obesity in Africa with 44% and 39% respectively. This study was done to assess the effect of the nutritional health education program on changing knowledge and attitude and practice towards nutrition of mothers during pregnancy and its role on gaining optimal weight. Methods: An interventional study (pre-posttest), in Zagazig University Antenatal Care Outpatient Clinic. Patients' criteria: 115 pregnant women in the first trimester, aged 18-35 years, Nonsmokers, take no medication and don’t have any chronic medical disorder with Body mass index (BMI) between 18.5 and 24.9 kg/m2 . Procedures: Data collection through a questionnaire of three parts; women’s characteristics, pretest and posttest, the health education sessions were applied on the pregnant women and the change was detected. Results: There was statistically significant difference in total knowledge from (66.5±28.9) to (117.6±25.3) and total attitude from (3.3±2.1) to (9.5±2.8) scores in the pregnant women after the nutritional education sessions with improvement from 45.5% to 80.5% and from 27.3% to 79.2% in knowledge and attitude respectively (p-value <0.001). The change in habits and practice was statistically significant (p-value <0.001). The average weight gain of the studied group was (16.1±8.5) kg ranged from 9 to 18 kg. Conclusion: The health education sessions were effective in improving pregnant women’s knowledge, attitude and practice. The healthy diet succeeded in improving gestational weight gain. Key words: weight gain; pregnant women; nutritional education sessions