Human leptin is identified as a 16kDa (146 amino acids) protein secreted from adipocytes which influences body weight homeostasis. In order to produce active leptin, the human obese gene coding for leptin was expressed in Bacillus subtilis WB600 strain which is deficient in six extracellular proteases. The recombinant leptin was produced in a culture supernatant, and in a culture supernatant, it was contained as high as 48% for total proteins. After simple purification steps, which consisted of ammonium sulfate precipitation and anion-exchange column chromatography, 2.3 mg of leptin with a purity greater than 95% was obtained from the 0.51 culture with the recovery yield of 38.3%. The purified leptin showed the correct folding structure with one disulfied bond.