Our study aims to explore the differences in functional connectivity in the nucleus accumbens (NAc) between patients with melancholic depression and non-melancholic depression (NMD) and their relation to melancholic depression's pathogenesis. We recruited 60 melancholic depression, 58 NMD, and 80 healthy controls, all matched for gender, age, and education. Functional connectivity analysis focused on bilateral NAc as the region of interest, comparing it with the whole brain and correlating significant differences with clinical scores. Melancholic depression patients showed reduced functional connectivity between the left NAc and anterior brain regions, and between the right NAc and temporal and frontal areas, compared to healthy controls. In contrast, NMD patients displayed reduced functional connectivity only between the left NAc and the posterior cingulate cortex. Melancholic depression patients also exhibited increased functional connectivity between the right NAc and the middle frontal gyrus, unlike NMD patients. The findings suggest that melancholic depression patients exhibit unique NAc functional connectivity patterns, particularly with the default mode network and prefrontal areas, suggesting atypical reward-circuitry interactions. The right NAc's connection to the prefrontal gyrus may distinguish melancholic depression from NMD.Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc.