Investigations into the beneficial effects of the interaction between plants and soil microorganisms towards bioremediation of contaminated soil has been studied over the past 30 years. This subject has been summarized as the process where organic contaminants can be removed from the soil through the interaction between roots and catabolic microbial populations. This study assessed the tolerance of different plant species against polycyclic aromatic hydrocarbon-non aqueous phase liquid (PAH-NAPL) contaminated soil and the feasibility of the use of their root biomass to promote the biodegradation of 14C-phenanthene. Toxicity results showed that seeds germination was not affected by the presence of PAHs. Furthermore, mineralisation of 14C-phenanthrene was significantly enhanced by the addition of root biomass after at least two weeks incubation. Moreover, bacterial numbers did not show a significant relationship with 14C-phenanthrene mineralisation. Results showed that the higher mineralisation of 14C-phenanthrene is not related to an increase on the microbial numbers as is normally assumed.