A low-temperature hydrocarbon-degrading strain T7-2, isolated from sea-mud of Bohai polluted area and identified as Rhodococcus erythropolis, was found to produce an extracellular, nondialyzable emulsifying agent (referred to as bioemulsifier) when grew with hexadecane as carbon source. The results showed that, this bioemulsifier which could remarkably emulsify hydrocarbons such as diesel oil, is consisted of three parts-carbohydrates, lipids and proteins, the proportion of which was 55.43:31.24:12.65. The monosaccharide compositions were identified as mannose and rhamnose; the lipid compositions included decanoic acid, lauric acid, hexadecanoic acid and stearic acid, and the protein constituents were composed of sixteen amino acids. Besides, according to the study of the physic-chemical properties of the bioemulsifier, it possesses the obvious advantages of character stability, high function efficiency and wide adaptation range, therefore this bioemulsifier is believed to have extensive application values for bioremediation of marine oil pollution, petroleum exploitation and etc.