Effects of petroleum contamination on counts,diversity and dominant populations of bacteria in paddy soils were investigated in the Shenfu Irrigation Zone,the largest zone irrigated with oilcontaining wastewater for more than 50 years in Northeast China.Bacterial genetic diversity was determined with 16S rDNA PCR-denaturing gradient gel electrophoresis(DGGE).Results show that total petroleum hydrocarbon (TPH) concentration in the paddy soil varied from 277 to 5 213 mg kg^-1 dry soil.Soil TPH concentration declined along with the distance of the irrigation channel from the water source,showing a gradient from upstream to downstream and was positively correlated with organic matter (r=0.691,p=0.057).At the current pollution level,the paddy soil TPH concentration was positively correlated with the CFU of aerobic heterotrophic bacteria (AHB) (r=0.928,p <0.001).While genetic diversity of the bacteria based on DGGE profiles was negatively correlated with TPH concentration (r=-0.715,p=0.013).Sequence analysis of prominent bands in DGGE profiles show that β and γ subgroups of Group Proteobacteria were dominant in paddy soil of the Shenfu Irrigation Zone,All or some of the populations may play a significant role in metabolizing the petroleum compounds.