The purpose of this study was to identify microbial strains that have a strong ability to biodegrade lubricating oil. No.20 lubricating oil was used as the sole carbon source in an isolation medium to screen bacteria from sludge that had been contaminated with crude oil. Through both morphological and biochemical methods, the bacterial strain that had the highest biodegrading capacity was identified as Zoogloea sp. On the basis of these preliminary results, a biological contact oxidation method was employed to further assess the ability of the Zoogloea sp. strain to treat wastewater contaminated by No. 20 lubricating oil using three oxidation cabins and two hydraulic retaining times (HRT). Results showed that the concentration of No. 20 lubricating oil with a 12 h hydraulic retaining time and 16.5 L h-1 inflow rate was reduced by99.3% in 15 d, and with a 6 h hydraulic retaining time and 33 L h-1 inflow rate it decreased by 98.6% in 12 d. The results from this study indicated that Zoogloea sp. had a strong potential to be utilized in biodegradation of lubricating oil.