OBJECTIVES: To investigate the effect of pachymic acid on brown/beige adipocyte differentiation and lipid metabolism in preadipocytes. METHODS: 3T3-L1 MBX cells were induced to differentiate into beige adipocytes using a brown cocktail method. The impact of pachymic acid on the viability of 3T3-L1 MBX cells was evaluated using the CCK-8 assay. The formation of lipid droplets following treatment with pachymic acid was observed by oil red O staining. The mRNA expression levels of key browning genes, including uncoupling protein (Ucp) 1, the peroxisome proliferator activated receptor-γ coactivator (Pgc)-1α, and the PR domain-containing protein 16 (Prdm16), as well as the mRNA expression of sterol regulatory element-binding protein (Srebp) 1c, acetyl-coA carboxylase (Acc), fatty acid synthase (Fas), and hormone-sensitive triglyceride lipase (Hsl), adipose triglyceride lipase (Atgl), and carnitine palmitoyltransferase (Cpt) 1 were detected by quantitative reverse transcription polymerase chain reaction. The protein expression of Ucp1, Pgc-1a, and Prdm16 was detected by Western blotting. RESULTS: The 3T3-L1 MBX cells were induced in vitro to form beige adipocytes with high expression of key browning genes(Ucp1, Pgc-1α, and Prdm16), and beige adipose-marker genes (Cd137, Tbx1, and Tmem26). Concentrations range of 0-80 μmol/L pachymic acid were non-cytotoxic to 3T3-L1 MBX cells. Pachymic acid treatment significantly inhibited the differentiation of 3T3-L1 MBX cells, resulting in a notable decrease in lipid accumulation. There was a marked increase in the expression of key browning genes and their proteins products, such as Ucp1, Pgc-1α, and Prdm16, while the expressions of fat synthesis-related genes Srebp1c, Acc and Fas were significantly decreased (all P<0.05). The expressions of lipolysis-related genes (Hsl, Atgl, and Cpt1) were significantly increased (all P<0.05). Treatment with 20 μmol/L pachymic acid showed the most pronounced effect. CONCLUSIONS: Pachymic acid can inhibit fat synthesis and promote lipid decomposition by regulating the brown formation and lipid differentiation of preadipocytes.