A dibenzo-p-dioxin-degrading bacterial strain, Rhodococcus opacus SAO101, was isolated from forest soil samples collected from the subtropical islands of Japan by enrichment of a mineral salt medium containing dibenzofuran as the sole carbon and energy source. The isolated bacterium could utilize dibenzo-p-dioxin as the sole carbon and energy source, and also many monocyclic aromatic compounds, such as toluene, phenol, and chlorobenzene, as well as bicyclic aromatic compounds, such as biphenyl, naphthalene, and dibenzothiophene. Furthermore, strain SAO101 has a high co-oxidative potential for chlorinated dibenzo-p-dioxin. Metabolite analysis of dibenzo-p-dioxin degradation by strain SAO101 revealed the formation of dihydrodiol, 2,2',3'-trihydroxybiphenyl ether, and a meta-cleavage compound of 2,2',3'-trihydroxybiphenyl ether, and the accumulation of dihydroxy compounds. On the basis of these results, the metabolic pathway of dibenzo-p-dioxin was proposed. This is the first report of the degradation of dibenzofttrans/dibenzo-p-dioxins by a Rhodococcus species.