Polyphenols have been shown to possess outstanding anti-obesity properties. In this study, the effect of blue honeysuckle berry extract (BHBE) with high polyphenol content on lipid accumulation in adipocytes and the underlying mechanism were investigated for the first time. Composition analysis demonstrated that flavonoids (mainly flavonols and anthocyanins) were the primary polyphenols in BHBE, which contributed to its biological functions. The results of Oil Red O staining combined with triglyceride (TG) content determination showed that BHBE exhibited an obvious inhibitory effect on intracellular lipid accumulation in a dose-dependent manner. BHBE also reduced the protein level of fatty acid synthase (FAS) and increased the phosphorylation level of acetyl-CoA carboxylase (ACC), indicating that lipogenesis was suppressed by BHBE treatment. Moreover, BHBE was found to significantly promote the phosphorylation of AMP-activated protein kinase (AMPK) and further reduce the expression of key transcription factors (PPARγ, C/EBPα, and SREBP-1c) that regulate lipogenesis. In addition, the expression of beige adipocyte markers (Tmem26 and Cd137) and uncoupling protein 1 (UCP1) was increased in BHBE-treated adipocytes. In summary, we consider that BHBE inhibits lipid accumulation in adipocytes by suppressing lipogenesis as well as by promoting beiging of adipocytes. These results support blue honeysuckle berry as a candidate functional food against obesity.