Polycyclic Aromatic Hydrocarbons (PAHS) are important pollutants which have toxic, carcinogenic and mutagenic properties and are considered as a serious hazard to human health and environment. Bioremediation of PAHs contaminated soil was studied in the soil slurry phase bioreactor. For enhancement of biodegradation, bioaugmentation (which is the process of adding microorganisms with the potential of pollution biodegradation to the bio-slurry reactor) was applied. Phenanthrene (C₁₄H₁₀), a three-benzene ring PAHs, was added in concentration of 100mg/kg soil. Two isolated species and consortium of bacteria were inoculated to the medium in density of 7×10⁷ CFU/mL. The analysis of variance (ANOVA) was used for finding of optimum levels of type of bacterial culture and presence effect of endogenous factors. The base of the bacteria was petroleum-contaminated soil from around Tehran petroleum Refinery. Control reactor (killed bacteria) showed 5% loss of phenanthrene and biodegradation in the non-augmented reactor (endogenous microorganisms) in a slurry bioreactor was about 17%. In the case of bioaugmentation with Pseudomonas.spp, Pseudomonas aeruginosa and consortium, phenanthrene degradation efficiency were 87.8%, 85.5% and 92.8% ,respectively, presenting the positive effect of biodegradation in consortium augmented compared to the isolated one. Colony forming units (CFUs) variation showed good conformity and agreement with the performance of the reactors with respect to phenanthrene degradation. Hence, the results of this experiment show that bioaugmentation may be considered as an effective method to enhance the bioremediation in removal of PAHs from contaminated soils.