A pilot batch study was performed to investigate the feasibility of using microemulsions to enhance the biodegradation of polycyclic aromatic hydrocarbons (PAHs). Oil in water (O/W) microemulsions composed of Tween-80, 1-pentanol and linseed oil significantly enhanced the apparent solubility of phenanthrene (PHE) up to 110.5 mg L-1 as compared to treatment with Tween-80 alone due to the additional solubilization of PHE in the oil phase of microemulsions, Batch incubation experiment showed that biodegradation of PHE by Bacillus subtilis B-UM in aqueous system was inhibited in the presence of Tween-80 while microemulsion composed of 0.4% Tween-80, 0.1% 1-pentanol and 0.05% linseed oil significantly enhanced its biodegradation up to 46.7% in 18 days. Natural composting of PAH contaminated soil on the other hand could remove 47.6% and 14.6% of PHE and benzo(a)pyrene (B[a]P) respectively while inoculation of B-UM together with the addition of Tween-80 increased the removal of B[a]P to 42.2%. The combined addition of microemulsion and inoculation of B-UM significantly increased the biodegradation of B[a]P and PHE with 63.6% and almost 100%, respectively. The results affirm that microemulsion is more effective than surfactants in facilitating the biodegradation of PAHs under thermophilic composting condition which provides a potential novel approach to remediate soil contaminated with PAHs.