Background: A great proportion of pregnant women gain weight above the recommendations of the Institute of Medicine (IOM), which is associated with adverse maternal and child health outcomes. We did not find any nutrition education intervention in this field and the available significant results are related to lifestyle trials. Thus, we examined the effect of a nutrition education intervention on gestational weight gain and adherence to IOM limits as the first study in this field. We surveyed the impact of the intervention on the birth anthropometric indices, as well. Methods: 192 pregnant mothers were recruited to this prospective randomized clinical trial from 15 health centers, five hospitals, and 15 private obstetrical offices in Isfahan. They were randomly divided into an intervention (n = 96) or a control (n = 96) group. Each woman met the same nutritionist at the time of enrollment for nutrition assessment and an individualized nutrition intervention plan was developed. Then, the nutrition education intervention including three 45 -60 min training sessions at 6 -10, 18, and 26 weeks of pregnancy was performed. Results: The proportion of excessive gestational weight gain (GWG) during pregnancy decreased in the interventional group (27.9% vs. 46.0%, P = 0.01). In addition, the mean of total GWG in the intervention group decreased significantly compared to the control