3,6′-Disinapoyl sucrose (DISS) is the active oligosaccharide ester component from roots of Polygala tenuifolia, and its antidepressant effects was found in the forced swimming test (FST) and tail suspension test (TST). We aimed to study the antidepressant effects of DISS in the chronic unpredictable mild stress (CMS) model in rats and explore the underlying mechanisms in the hypothalamic-pituitary-adrenal (HPA) axis. We found that when subjected to the chronic stress protocol for 28 days, animals showed reduced sensitivity to reward and abnormality in the HPA axis. DISS (10 or 20 mg/kg, i.g.) improved the reward reaction as measured by increasing sucrose consumption, remarkably reduced serum CORT, ACTH and CRH levels in the CMS-treated rats. In addition, DISS enhanced the expression of glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) mRNA. These results indicated that the antidepressant effects of DISS in chronically stressed animals might relate to the modulating effects on the HPA axis, which might be an important mechanism for its antidepressant effect.