INTRODUCTION: Flavan-3-ols (FLs), astringent polyphenols, are known to have low bioavailability and induce excessive sympathetic nervous system activation. This study aimed to compare the effects of FLs on brown, subcutaneous, and visceral adipose tissue in mice. METHODS: C57BL/6J male mice fed a standard or high-fat diet were given water or 50 mg/kg FL orally by gavage for 2 weeks. Excised brown, inguinal, and epididymal fat tissues were prepared for frozen sectioning. After hematoxylin and eosin (HE) staining, the effects of FL administration on each adipose tissue were observed, and expression analysis of mitochondrial DNA genes was performed. RESULTS: Repeated administration of FL had no morphological effects on brown adipose tissue or visceral fat. However, FL significantly reduced the cell size in subcutaneous fat and induced the appearance of multilocular structures. Furthermore, FL increased cytochrome B expression in subcutaneous fat. The results showed that FLs induce browning of subcutaneous fat in mice. CONCLUSION: This study showed that FL-induced enhancement of sympathetic nerve activity increased mitochondria in subcutaneous fat and promoted browning. However, no changes were observed in other adipose tissues. Further long-term administration is required to analyze the effects of FLs on adipose tissue thoroughly.