Adult attachment style (AAS) refers to individual differences in the way people experience and regulate their social relationships and corresponding emotions. Based on developmental and psychological research, it has been hypothesized that avoidant attachment style (AV) entails deactivating strategies in social contexts, whereas anxious attachment style (AX) involves hyper vigilance and up-regulation mechanisms. However, the neural substrates of differences in social emotion regulation associated with AAS have not been systematically investigated. Here we used fMRI in 19 healthy adults to investigate the effect of AAS on the processing of pleasant or unpleasant social and nonsocial scenes. Participants were asked either to naturally attend (NAT), cognitively reappraise (REAP), or behaviorally suppress (ESUP) their emotional responses. Avoidantly attached participants showed increased prefrontal and anterior cingulate activation to social negative scenes when making spontaneous emotion judgments. They also exhibited persistent increases in dorsolateral prefrontal cortex and left amygdala activity for the same stimuli during reappraisal, as well as additional activation in supplementary motor area and ventral caudate during the suppression of social positive emotions. These results suggest that AV may imply less efficient reappraisal strategies to regulate social negative emotions, and lead to higher conflict or effortful control when suppression cannot be employed. In contrast, anxiously attached participants showed differential increases in the right amygdala and left parahippocampal cortex for social negative and positive stimuli, respectively, but only when making spontaneous emotion judgments. No effect of AX was found during down-regulation conditions. This suggests heightened arousal to negative information without difficulty in down-regulating emotions through cognitive re-evaluation or suppression. Taken together, these findings reveal for the first time the neural underpinnings of attachment-related differences in social emotion regulation.