Seven strains isolated from DSO (disulfide oil) contaminated soils. Among them, two strains had high potential to remove DSO from contaminated soils. These strains identified as Paenibacillus (a gram positive, nitrogen fixing spore, spore forming bacillus) and Rhodococcus (a gram positive, catalase positive, acid fast forming bacteria), by preliminary tests. The optimal conditions for DSO removal from contaminated soils were determined. The biotic depletion for Paenibacillus pre-grown in nutrient broth was 24.3% and for Rhodococcus was 19.3%. Bioremediation of DSO in soil was investigated by gas chromatography and UV-vis absorption spectroscopy techniques. The results showed that addition of water (20 mu l/g soil) to soil is necessary for DSO removal by both strains and none of the strains could remove DSO in concentrations more than 30 mu g/g soil. The results also showed that none of these strains could degrade DSO under anaerobic condition. (c) 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.