Such petroleum hydrocarbons as ethylene oligomer are among soil and water pollutants. Physical and chemical methods employed in elimination of these pollutants, in addition to being inefficient, are damaging to the environment too. Throughout the present research, powerful decomposer isolates, namely: Lysinibacillus xylanilyticus (a bacterium isolate), and Aspergillus niger (a fungal isolate) were separated (through culture enrichment) from landfill soils). The capability of these isolates to degrade ethylene oligomer as the sole source of carbon was evaluated in liquid mineral media containing 1% ethylene oligomer followed by incubation on a rotary shaker at 30°C for 30 days. Based upon this issue, fungal biomass was assessed as 0.1370 g per 100 ml culture medium. Moreover, a 3.2-fold increase in culture concentration was observed in comparison with initial culture concentration of 1.5×108 CFU.ml-1 in the bacterium culture indicating the utilization of ethylene oligomer as the sole source of carbon. FTIR analysis confirmed ethylene oligomer oxidation and formation of carbonyl groups by the isolates during the oxidation process.