For the development of biocatalysts and processes for microbial desulfurization of petroleum, more than 60 microbial strains capable of DBT(Dibenzothiophene) degradation were isolated from oil-polluted soils through 3 months of continuous and enrichment cultures. Among them, A23-3 strain could grow on DBT as the only sulfur source, while hexadecane was not utilized as a carbon source. The rate of desulfurization by A23-3 in a DBT-glucose medium was satisfactory. The addition of yeast extract or trace metal solution accelerated the rate of desulfurization about 4.5∼6.5 times. In case of actual diesel oil treatment, the specific rate of DBT degradation was 0.045g-DBT per g-cell · hour. A number of aromatic compounds heavier than C_l4 in diesel oil were also degraded by A23-3. A23-3 strain was evaluated as a good catalyst for the production of low-sulfur, low-aromatic clean diesel oil.