Abstract: Objective To study the possible mechanism of medium chain fatty acid (MCFA) in reducing body weight and body fat mass by observing the effect of MCFA on expression of transcription factor mRNA in adipose tissue of obese mice. Methods Thirty C57BL/6J obese mice were randomly divided into MCFA group and long chain fatty acid (LCFA) group (15 in each group)according to their fasting body weight. Twelve weeks after they were fed with high fat diet containing 2% MCFA or LCFA, their body, liver, and mesenteric, epididymal, perirenal fat pads were weighed and their body heights were measured. Protein, peroxisome proliferators-activated receptor-γ(PPAR-γ) and tumor necrosis factor-α(TNF-α) levels in white adipose tissue (WAT) were measured by BCA and ELISA, respectively. Expressions of PPAR-γ, sterol regulatory element-binding protein-1(SREBP-1)and CCAAT enhancer binding protein-α(C/EBP-α) mRNA in WAT were detected by RT-PCR. Results The body, liver, and mesenteric, epididymal, perirenal fat pads were significantly lighter whereas the expression levels of TNF-α, SREBP-1 and C/EBP-α mRNA in WAT and the body height were significantly lower in the MCFA group than in LCFA group (P＜ 0.05). No significant difference was found in PPAR-γ mRNA expression level between the two groups (P＞ 0.05). Conclusion MCFA can inhibit the differentiation of adipocytes by down-regulating the expression levels of TNF-α, SREBP-1 and C/EBP-αmRNA in adipose tissue.