Background: Food aid programs are strategies that aim to improve nutritional status and to tackle food insecurity. This study aimed to evaluate the effect of a National Food Supplementary Program for Children on households′ food security. Methods: The study sample included 359 mothers of children aged 6-72 months under the coverage of the program in two provinces of Iran. Demographic and socioeconomic characteristics of the households and percentage of supplementary food items consumed by target child were assessed by a questionnaire and checklist. Data on household food security were collected by locally adapted Household Food Insecurity Access Scale at the baseline of the study and 6 months thereafter. Results: At the baseline, only 4.7% of families were food secure, while 43.5% were severely food insecure, and these proportions were changed to 7.9% and 38%, respectively (P < 0.001), at the end of the study. Odds of having worse food insecurity in households with medium and high wealth index was 65% and 87% lower than those with low wealth index, respectively (odds ratio [OR] = 0.35, 95% confidence interval [CI]: 0.2-0.61, and OR = 0.23, 95% CI: 0.12-0.43). Food sharing was common among more than 95% of the studied households. Mean maternal body mass index (BMI) increased significantly after 6 months (P < 0.001). However, there was no significant association between mother′s BMI and household food security in the baseline and at the end of the study (P > 0.05). Conclusions: Findings show that the food supplementary program for children can also improve the household food security status. Further research is needed to assess other factors that affect the effectiveness of this kind of programs.