As the preschool years are a formative period for long-term physical and mental health, this period is recognised as an important window for early effective intervention. Parenting behaviour is a key factor to target in order to optimise child development. Group-based interventions for parents are considered efficient and cost effective methods of early intervention and have been found to improve child behaviour and adjustment. Self-efficacy is key to behaviour change and as such parental self-efficacy should be a consideration in interventions aimed at influencing parenting behaviour. Therefore, the purpose of this systematic review was to examine the impact of group-based early interventions for parents of preschool children on parental self-efficacy. Nine databases were searched (ASSIA, CINAHL, EMBASE, Maternity and Infant Care, Ovid Medline, PsycINFO, Pubmed, Science Direct and Web of Science). Studies were included if they were a randomised controlled trial of a group-based intervention for parents of preschool children and measured change in parental self-efficacy. Fifteen studies were identified. Although changes in parental self-efficacy following a group-based intervention were noted in the majority of studies reviewed, the methodological quality of the studies included in the review means these findings have to be interpreted with caution; only seven studies were rated to be methodologically adequate. Further research is needed to understand the mechanisms by which these interventions may improve parental self-efficacy. Studies specifically examining the impact of such interventions on paternal self-efficacy are also warranted.