Diethyl phthalate (DEP) is a representative of phthalate esters (PAEs) that are largely used as industrial additives and have become environmental contaminants and endocrine disruptors. A newly isolated bacterial strain Sphingobium yanoikuyae SHJ was found to be capable of degrading DEP very efficiently. Four intermediates during the DEP degradation process were identified to be ethyl methyl phthalate (EMP), monoethyl phthalate (MEP), monomethyl phthalate (MMP) and phthalic acid (PA) using high-performance liquid chromatography tandem high-resolution mass spectrometry (HPLC-HRMS). When there was limited oxygen under SSA conditions, the rates of the further degradation of MEP and PA were slower compared to that under aerobic conditions. Although all intermediates EMP, MEP and MMP eventually decreased or disappeared, the DEP degradation kinetics showed that EMP formed much faster than that of MEP, and MMP appeared after the decreasing of MEP. It is proposed that two DEP degradation pathways must be present in S. yanoikuyae SHJ. The first is DEP -> MEP -> PA through a sequential hydrolysis process. The second is DEP -> EMP -> MEP -> MMP -> PA through a combination of demethylation or trans-esterification with methanol and hydrolysis processes. It is concluded that S. yanoikuyae SHJ has a versatile capability of degrading DEP and will have a great application potential in bioremediation of PAEs-contaminated shallow aquifer.