Uncoupling proteins are the mitochondrial inner membrane proteins regulating basal metabolism. UCP3 in muscle and adipose tissue helping metabolism and fat oxidation affecting thermogenesis, involve in fatty acid metabolism and energy homeostasis. 42 adult rats divided into 6 groups including control group, the high-fat diet Obese group, experimental groups that in addition to the high-fat diet received 50,100,200 mg/Kg doses of cinnamon extract and the sham group with 200 mg/Kg extract treatment . RNA extracted from muscles, cDNA synthesized and UCP3 gene expression level was examined by real-time PCR. In muscls of Obese rats significant decrease in UCP3 gene expression was observed but in exprimental groups there was significant increased level of UCP3 gene expression in 100, 50mg/Kg dose of treatment.UCP3 might be a target for pharmacological up regulation in treatment of obesity. Cinnamon might influence UCP3 expression, in a dose dependent manner and low dose was more effective.