Introduction: Breastfeeding is one of the most important health-promoting behaviors and one of the main goals of the World Health Organization. Breastfeeding self-efficacy is an important variable in predicting the duration of breastfeeding and its continuation. Breastfeeding self-efficacy is a modifiable parameter that is affected by various individual and social factors. Objective: This study aimed to compare breastfeeding self-efficacy levels of mothers with different ages referred to comprehensive health centers. Materials and Methods: This is a correlational study with a cross-sectional design. Study samples were 460 breastfeeding mothers of different ages referred to comprehensive health centers in Rasht City, Iran in 2019. The data collection tool was a two-part questionnaire: A demographic form and a breastfeeding self-efficacy scale-short form (BSES-SF). Data analysis was performed using the independent t-test, Analysis of Variance (ANOVA), and regression. Results: The Mean± SD scores of breastfeeding self-efficacy were as follows: 43. 69± 12. 48 in mothers under 19 years old, 50. 26± 10. 93 years in mothers aged 19-35 years, and 58. 35± 8. 53 years in mothers over 35 years old. There were statistically significant relationships between breastfeeding self-efficacy and maternal age (P=0. 0001), housing status (P=0. 0001), monthly income (P=0. 0001), breastfeeding history (P=0. 0001) and source of breastfeeding education (P=0. 014), number of pregnancies (P=0. 0001) and number of deliveries (P=0. 0001). The variables of maternal age (β =4. 130, P=0. 0001, 95%CI; 2. 165-6. 051), monthly income (β =1. 735, P=0. 002, 95% CI; 1. 239-3. 922), breastfeeding history (β =5. 505, P=0. 0001, 95%CI; 4. 598-9. 183) and number of pregnancies (β =3. 553, P=0. 0001, 95%CI; 1. 278-4. 098) were predictors of breastfeeding self-efficacy. Conclusion: Breastfeeding self-efficacy increases with the older age and its level is lower in mothers aged < 19 years than in other age groups. Counseling support for mothers at this age is more necessary, and the need-based educational program should be designed for them.