Abstract:[Objective] A thermophilic hydrocarbon-degrading strain DM-2, isolated from Shengli oilfield and identified as Geobacillus stearothermophilus, produced an extracellular bio-emulsifier. [Methods] To characterize the bio-emulsifier, its chemical composition was determined by colorimetric method, infrared spectroscopy, HPLC and amino acid automatic analyzer. [Results] The bio-emulsifier is consisted of polysaccharides (71.4%, W/W) and polypeptide (27.75%, W/W). It could emulsify diesel, benzene, xylene and kerosene. It tolarated high temperature, salt and pH. [Conclusion] The bio-emulsifier produced by strain DM-2 is a novel bio-emulsifier and has potential applications in the oil exploitation, oil recovery and transportation, oil tank cleaning, and oil pollution regulation.