An oilcontaminated groundwater sample was collected at an abandoned petrochemical factory. Bacterial genome DNA was extracted for the 16S rDNA gene amplification, and then a bacterial 16S rDNA gene clone library was constructed. After the phylogenetic analysis of 16S rDNA sequences, bacterial diversity and community structure of the groundwater were studied. The results showed the bacteria in the groundwater could be divided into 11 groups, which were as follows:Betaproteobacteria(381％),Alphaproteobacteria(353％),Gamaproteobacteria(51％),Deltaroteobacteria(52％),Bacteroidetes(40％),Verrucomicrobia(25％),Epsilonproteobacteria(19％),Nitrospira(13％),Planctomycetes(13％),Candidate Division OD1(13％),Unclassified Bacteria(38％)。Betaproteobacteria and Alphaproteobacteria were predominant in the ecosystem, each of which accounted for over onethird of total clones. Hydrogenophaga and Sphingomonas are the most abundant degrading bacteria in the sample, which accounted for 381％ and 353％ of all bacteria respectively. Many clones also affiliated with other degrading bacteria, such as Sulfuricurvum kujiense, Trichlorobacter thiogenes, Rhodoferax ferrireducens and bacteria of genus Rhodobacter, Methylomonas, Nevskia. Besides, a lot of 16S rDNA sequences in the clone library had high similarity to the ones originated from similar polluted environments, such as groundwater contaminated with tar oil, groundwater contaminated with benzene, soil contaminated with crude oil, soil contaminated with methyl bromide and methyl chloride, antibiotics production wastewater and activated sludge, which proved that there were lots of degrading bacteria population in the oilcontaminated water. The components of petroleum contaminant have an important effect on community structure of degrading bacteria.
