Abstract: In the present study a trial was carried out to develop a new biotechnique for removal some toxic substances from edible oils as affected by deep-fat frying operation. Wastewater samples from Oil and Soap Company was used as a source of oil using bacteria and very simple technique for treatment the deep-fat frying oils with bacterial isolates was applied. A decrease in many toxic and/or carcinogenic compounds was observed in treated oils included free fatty acids (FFA), peroxide value (PV), malonaldehyde (MDA) and benzo(a)pyrene B(a)P contents by different rates. The rates of decreasing were increased with the increasing of oil concentration in cultural medium of used bacteria up to 15%. Spectroscopic analysis showed that many absorbance peaks 3420, 3120, 1750 and 970-1000 nm have been disappeared which means the removal of many corresponding toxic compounds included hydroperoxides, polymerization products, carbonyl groups or acids and trans-ethylenic double bonds of fatty acids as the result of treatment by Bacillus firmus. Results suggested that this biotechnique could be adequately coordinated with the commercial concern and the interests of society or the administration, which aim to improve consumer safety.