Aims To evaluate the effects of a breastfeeding intervention on primiparous mothers' breastfeeding self‐efficacy, breastfeeding duration and exclusivity at 4 and 8 weeks postpartum. Background Few studies have examined the effects of breastfeeding self‐efficacy on improved breastfeeding outcomes among primiparous mothers in China. Design An experimental pre‐test and posttest, two‐group design was used in the study. Methods A total of 74 participants were recruited to the study from a tertiary hospital in central China, from June–October 2012. An individualized, standardized nursing intervention based on the Self‐Efficacy Theory was delivered to enhance mothers' breastfeeding self‐efficacy, breastfeeding duration and exclusivity at 4 and 8 weeks postpartum. Participants were randomly assigned to an intervention or referent group. Participants in the intervention group received three individualized, self‐efficacy‐enhancing sessions. Participants in the referent group received standard care. Results Participants in the intervention group showed significantly greater increases in breastfeeding self‐efficacy, exclusivity and duration than participants in the control group at 4 and 8 weeks postpartum (except for duration at 4 weeks). High baseline breastfeeding self‐efficacy predicted higher breastfeeding self‐efficacy later and more exclusive breast‐feeding. Conclusion The findings in this study suggest that intervention aimed at increasing self‐efficacy has a significant impact on maternal breastfeeding self‐efficacy and short‐term breastfeeding outcomes.