BackgroundThe exclusive breastfeeding condition in China is not optimism now. Maternal breastfeeding self-efficacy stands as a pivotal factor influencing exclusive breastfeeding. Interestingly, studies have suggested that father support breastfeeding self-efficacy is a pivotal mediator in infant breastfeeding. Thus, the current research aimed to investigate the association between father support breastfeeding self-efficacy and exclusive breastfeeding at six weeks postpartum, and the influencing factors of father support breastfeeding self-efficacy.MethodsThis research was structured as a multi-centre cross-sectional study, involving 328 fathers, whose partners were six weeks postpartum, and recruited from two public hospitals in Southeast China. Self-designed demographic questionnaires, namely, Father Support Breastfeeding Self-Efficacy Scale-Short Form, Breastfeeding Knowledge Questionnaire, Positive Affect Scale and the 14-item Fatigue Scale, were applied. Descriptive statistics, Chi-square test, logistic regression univariate analysis and multiple linear regression were used to analyse data.ResultsResults indicate a significant difference between the infant feeding methods at six weeks postpartum and fathers with different levels of support breastfeeding self-efficacy (p < 0.05). Particularly, father support breastfeeding self-efficacy positively affected exclusive breastfeeding at six weeks postpartum after adjusting all the demographic characteristics of fathers (OR: 2.407; 95% CI: 1.017–4.121). Moreover, results show that the significant influencing factors of father support breastfeeding self-efficacy include breastfeeding knowledge, fatigue, positive affect, successfully experienced helping mothers to breastfeed, spousal relationships and companionship time.ConclusionsHigh-level father support breastfeeding self-efficacy effectively increased exclusive breastfeeding rate at six weeks postpartum. To enhance the exclusive breastfeeding rate, nurses or midwives can endeavour to design educational programmes or take supportive interventions customised for fathers, such as enhancing their breastfeeding knowledge education, reducing fatigue and mobilising positive emotions, thereby bolstering paternal self-efficacy in breastfeeding.