A long-chain n-alkane-using microorganism was isolated from a soil sample, and was identified to belong to genus Acinetobacter. This strain, Acinetobacter sp. strain M-1, grew on n-alkanes ranging in carbon length from C13 to C44 as a sole carbon source. This strain could grow on the solid hydrocarbons without addition of any detergents. The growth and the hydrocarbon use were enhanced by the addition of a surface active agent, Plysurf A210G.