Aim :Methodology : Results :Interpretation :The aim of this study was to isolate, identify and characterize diethyl phthalate degrading bacterial strains isolated from a crude oil contaminated soil from a landfill dump site of a petroleum refinery in Mersin, Turkey.The bacteria was isolated from a crude oil contaminated soil and characterized by 16S rRNA analysis. Bacterial genomic DNA was identified by 16S rRNA analyses. Biodegredation experiments were conducted for 5 days and plasmid curing experiment was performed. Catechol test was carried out to determine phthalate degradation pathways.The isolated bacteria from soil were identified as Pseudomonas putida based on 16S rRNA sequences. The size of the plasmid was estimated to be about 15.9 kb. Results of biodegradation experiments indicated that the diethyl phthalate concentrations were reduced by 85.5% after 5 days of incubation at pH 7.0 and 30°C. The ability of P. putida degrading diethyl phthalate was found to be plasmidmediated through curing experiments.The study suggested that plasmid of Pseudomonas putida PAG5 could be involved in effective degradation of diethyl phthalate.