The present invention relates to a novel microbial strain, Alteromonas sp. SN2 (KCTC11700BP) having an activity for degrading polycyclic aromatic hydrocarbon (PAH), a bioremediation process of polycyclic aromatic hydrocarbon (PAH) contaminants, comprising contacting a microbial strain Alteromonas sp. with PAH, and a composition for purifying polycyclic aromatic hydrocarbon (PAH) contaminants, comprising a microbial strain Alteromonas sp. It is advantageous that the present invention may be suitably utilized in treatment or remediation of oil contaminants, particularly naphthalene soil contaminants without production of a secondary contaminant source. As the strain and bioremediation process of this invention could be industrially utilized through low-cost and environment-friendly process, the present technology also may be carried out much more economically and efficiently than conventional technologies such as thermal technology, solidification technology, and vapor extraction technology.