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. Methods and Materials: 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 (b= 4.130, P= 0.0001, 95% CI; 2.165-6.051), monthly income (b = 1.735, P = 0.002, 95% CI; 1.239-3.922), breastfeeding history (b= 5.505, P = 0.0001, 95%CI; 4.598-9.183) and number of pregnancies (b= 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.