The effects of the inoculant strain Paracoccus aminovorans HPD-2 (isolated from a PAH-contaminated soil) on the bioremediation of the PAHs-contaminated soil and the structure of microbial communities in the soil were studied in soil microcosms. After inoculation for 14 days, 22.9% of total PAHs were removed from the soil in the treatment with the addition of 20% (v/m) bacterium suspension. The removal of 3-rings PAHs (36.1%) was higher than that of 5-rings (26.0%) and 4-rings PAHs (20.9%). The highest degradation of PAHs occurred in phenanthrene, anthracene, and benzo[a]pyrene. Bacterial population in the soil increased during the bioremediation process, but the population of actinomycetes and fungi changed insignificantly. Denaturing gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction (PCR)-amplified bacterial 16S rRNA gene fragments revealed that HPD-2 became into the dominant bacterial group in the soil with the addition of the bacterium suspension. These results indicate that HPD-2 is a promising candidate for bioremediation of PAHs-contaminated soils.