A symbiotic bacterium was idnetified from the etomopathogenic nematode, Steinernema carpocapsae, collected in Korea and its biological significance was examined for insecticidal and antibiotic effects. The symbiotic bacterium was isolated from the nematode-infected hemolymph of the fifth instar larvae of Spodoptera exigua. The intra-hemocoelic injection of the bacterial isolates killed the insect hosts within 24h. Several biochemical and morphological characters of the bacterium were identical to those of Xenorhabdus nematophilus. The bacterial growth was not showed antibacterial effects on containing 4,000 ppm of streptomycin sulfate or 2,000 ppm of penicillin. They showed antibacterial effects on Escherichia coli, Ralstonia solanacearum and Pseudomonas aeruginosa, but not on Pseudomonas putida and Pseudomonas fluorescens.