Aims and objectives. To examine the relationships between social support, maternal parental self-efficacy and postnatal depression in first-time mothers at 6 weeks post delivery. Background. Social support conceptualised and measured in different ways has been found to positively influence the mothering experience as has maternal parental self-efficacy. No research exists which has measured the relationships between social support, underpinned by social exchange theory and maternal parental self-efficacy using a domain-specific instrument, underpinned by self-efficacy theory and postnatal depression, with first-time mothers at 6 weeks post delivery. Design. A quantitative correlational descriptive design was used. Method. Data were collected using a five-part questionnaire package containing a researcher developed social support questionnaire, the Perceived Maternal Parental Self-Efficacy Scale and the Edinburgh Postnatal Depression Scale. Four hundred and ten mothers completed questionnaires at 6 weeks post delivery. Results. Significant relationships were found between functional social support and postnatal depression; informal social support and postnatal depression; maternal parental self-efficacy and postnatal depression and informal social support and maternal parental self-efficacy at 6 weeks post delivery. Conclusion. Nurses and midwives need to be aware of and acknowledge the significant contribution of social support, particularly from family and friends in positively influencing first-time mothers' mental health and well-being in the postpartum period. The development of health care policy and clinical guidelines needs to define and operationalise social support to enhance maternal parental self-efficacy. Relevance to clinical practice. These findings suggest that nurses and midwives need to be cognisant of the importance of social support for first-time mothers in both enhancing maternal parental self-efficacy and reducing postnatal depressive symptomatology in the early postpartum period.