Sphingomonas sp. P2 isolated from lubricant contaminated soil is capable of utilizing phenanthrene and several other PAHs. This strain is also co-metabolize high molecular weight PAHs such as fluoranthene and pyrene in liquid medium supplemented with phenanthrene. However, its growth and PAHs degradative abilities were inhibited after added to non-sterile soil. To improve its survival and PAH degrading activities, the study acclimatized Sphingomonas sp. to soil conditions before added to non-sterile soil microcosms. Soil acclimatization process was carried out by sequential cultivating of Sphingomonas sp. P2 in soil extract media and sterile soil. The acclimatized bacteria were used as inoculum for PAH bioremediation. Sphingomonas sp. P2 cultured in soil extract mixed with water (1:3) showed the highest PAHs degradative ability and survival efficiency in 2-g sterile microcosm when compared with other media. Soil extract mixed with water (1:3) was therefore selected as media for preparing liquid inoculum. Later, soil inoculum was prepared by adding the liquid inoculum into sterile soil spiked with phenanthrene. PAH bioremediation treatments were conducted in 20-g non-sterile soil microcosms to study the survival and PAHs degradability of acclimatized bacteria. Two types of microcosms with different concentrations of phenanthrene were used; (a) 100 ppm phenanthrene mixed with 100 ppm pyrene and (b) 300 ppm phenanthrene mixed with 100 ppm pyrene. The efficiency of soil inoculums preincubated for 4, 8 and 12 days and liquid inoculum prepared in soil extract mixed with water (1:3) were compared. The result showed that soil inoculum was able to degrade phenanthrene and could survive in non-sterile soil microcosms. Meanwhile, liquid inoculum was also effective in phenanthrene degradation especially at the beginning of the experiment. There was no significant difference in pyrene degradation between the treatments and control (without inoculum). 16S rDNA-DGGE analysis showed DNA band corresponding to Sphingomonas sp. P2 in all gels. The results suggested that the inoculated bacteria were one of the dominant populations in soil microcosms. Moreover, liquid and soil inoculum provided similar effects on soil bacterial populations