Background Optimal breastfeeding practices can help prevent under‐nutrition among under five children and WHO recommends Exclusive breastfeeding (EBF) for the first half of infancy. Rates of EBF are however low globally with Kenya at 61.2% against the projected rate of 80% by end of 2017. Aims Factors that may influence the success of EBF interventions are unclear. The study aimed at assessing the effect of a structured nutrition education intervention (SNEI) on maternal breastfeeding self‐efficacy (BSE) and EBF. Methods A cluster randomized study in which pregnant mothers attending two health facilities (Mangongeni and Kiandutu) in a resource restricted urban area of Thika –West, Kenya were randomized into either intervention or comparison groups. Maternal BSE was assessed at baseline (34 weeks) at midline (37 weeks) and at 6 months post‐partum using the Dennis cindy breastfeeding self‐efficacy scale‐short form (BSES‐SF).Those in the intervention went through four sessions of a structured nutrition education intervention (SNEI) that sought to improve BSE and taught the importance of EBF. Results There were no significant differences at 34th weeks gestation between the intervention versus comparison groups in the BSE scores but the findings were significant at midline and end‐line (t=3.816, df 351 p=0.001, t=4.095, df 316 p=0.001) respectively. The intervention had an effect on BSE. p=0.001 (log odds 2.089 and 95% CI of 0.823‐3.356). The survival distributions for the two groups were significantly different, log rank 20.277, (1, n=314) p < 0.001 for duration of EBF at 6 months post‐partum. Those in the intervention were more likely to EBF, p=0.008 (OR 0.17 95% CI of 0.05‐0.62). Conclusions and Recommendations A SNEI can improve BSE scores during anti‐natal clinics and BSE is predictive of EBF duration. Health care providers can use the BSES‐SF to identify mothers with low BSE scores and design interventions to assist in promoting EBF.