Biofilms are a multiple groups of microorganisms that attached to liquid surface or hardsurface objects to create a surface layer. In comparison with planktonic type, microorganisms found in this layer have higher tolerance for harsh conditions, better support for metabolism and reduce the competitiveness of other microorganisms. Therefore, application of biofilms in wastewater treatment and cleaning up oil pollution is a new, highly potential direction. In this study, the authors reported two bacterial strains DGD4 and DGD7 isolated from petroleum storage tank in Duc Giang, Gia Lam, Hanoi that were capable of biofilm formation and diesel degradation as well. The optimal conditions for biofilm formation by these two strains were temperature in the range 30 - 37°C, pH 7, the addition of maltose and yeast extract as carbon nitrogen sources, respectively. Standing incubation of biofilms formed by strains DGP4 and DGP7 in Gost mineral salt medium supplemented with 2 percent diesel oil resulted in 72,2 and 50,2 percent removal of of total diesel oil, respectively after 7 days. The results showed that biofilms formed by two strains have high diesel oil degradation capacities
therefore it is necessary to study on the total diesel degradation by the multi-species biofilm and carrier materials to improve the treatment of diesel oil-polluted wastewater.