Social decision-making tasks involve psychological processes key to effective functioning in a complex, social world. The Ultimatum Game (UG) is a widely studied social decision-making task, which models responses to fairness. A number of neuroimaging studies have investigated the UG to identify neural correlates of unfairness and decisions to reject versus accept an offer. We present the first quantitative summary of neuroimaging studies in social decision-making with a meta-analysis of 11 fMRI studies of the UG, including data from 282 participants. Effect-Size Signed Differential Mapping was used to estimate effect sizes from statistical parametric maps and reported peak information before meta-analysing them. Consistent activations were seen in the anterior insula, anterior cingulate cortex (ACC), supplementary motor area (SMA) and cerebellum in response to unfair offers. Robust activations in the ACC, SMA and putamen were seen when deciding to reject rather than accept UG offers. These are consistent with models of motivational conflict during the UG decision-making process, a response to norm violations, with a possible role for the reward system.