Understanding the impact of polycyclic aromatic hydrocarbons (PAHs) on soil environments is of increasingly important concern. Therefore, the microbial degradation of PAHs in soils has drawn considerable attention, but little is known about the PAH degradation genes in urban soils. In this study, we examined the diversity and abundance of the PAH degradation bacteria and evaluated whether the specific bacteria can reflect PAH contents in the soils from urban roadsides directly receiving traffic emission. The results of phylogenetic analysis indicated that low PAH degradation bacterial diversity occurred in the urban roadside soils, only including Mycobacterium sp., Terrabacter sp., and one novel cluster. The community composition diversity of PAH degradation bacteria did not show a significant difference across the sampling sites. The abundance of PAH degradation genes ranged from 5.70 x 10(6) to 6.44 x 10(7) gene copies g(-1) dry soil, with an average abundance of 1.43 x 10(7) gene copies g(-1) dry soil, and their spatial variations were related significantly to PAH contents in the soils. The Mycobacterium sp. was the most widely detected and estimated to occupy 65.9-100 % of the total PAH degradation bacteria at most of the soil samples, implying that the Mycobacterium sp. might play a primary role in degrading PAHs in the contaminated urban soil environments.