Resting cell assay and soil microcosms were set up to investigate the biodegradation capability and metabolic intermediate of polychlorinated biphenyls (PCBs) by a rhizobial strain Sinorhizobium meliloti. Biodegradation was observed immediately after 2,4,4'-TCB was supplied as a sole source of carbon and energy in liquid cultures. After 6 days, the percent biodegradation of 2,4,4'-TCB was 77.4% compared with the control. The main intermediate was identified as 2-hydroxy-6-oxo-6-phenylhex-2,4-dienoic acid (HOPDA) for 2,4,4'-TCB as determined by gas chromatography-mass spectrometry (GC-MS). Inoculation with S. meliloti greatly enhanced the degradation of target PCB mixtures in the soil. Moreover, soil culturable bacteria, fungi and biphenyl degrading bacteria counts showed significant increase after inoculation of S. meliloti. This study suggests that S. meliloti is promising in PCB bioremediation.