Background and Objectives: Pregnancy is the most significant stage of a woman's life which is accompanied with increased nutritional needs. This study aims to determine the effect of training program on the base of social cognitive theory constructs in order to improve nutritional behavior among pregnant women.
 Materials & Methods: This quasi-experimental study was conducted on 96 pregnant women in three zones of Tabriz city in 2015. In every zone, one health center was randomly assigned as intervention group and the other as control group (n=48 per group). Training program was applied on intervention groups for two months. Data were collected using a self-administered questionnaire with items on the social cognitive theory constructs and nutritional behavior questionnaire which was completed before and two months after intervention. Data was analyzed through SPSS-20 software by using independent t-test, paired t-test, chi-square, McNemar and fisher exact test.
Results: Results showed that scores of knowledge, outcome expectancy, expectations, self-efficacy, social support, self–regulations, reciprocal determinism and nutritional behaviors were increased significantly in the experimental group (P<0.001). Also, means of intake scores of folic acid, iron, multivitamins, and the number of daily servings of bread and cereals, dairy products, fruits and vegetables were significantly higher in the experimental group rather than the control group after intervention (P<0.001).
Conclusion: Implementation of educational intervention based on Social Cognitive Theory structures can be an effective role in modifying pregnant mothers' nutritional behavior.