The comparison of 16S DNA sequences of several strains of Xenorhabdus extracted from two strains of Steinernema carpocapsae (Russia), three strains of S. feltiae from Europe and Asia (Armenia) and two not described steinernematid species (USA and Cameroon) revealed high level of nucleotide differences between the bacteria originating from different nematode species and nearly complete identity of bacteria from conspecific nematode strains. Thus, Xenorhabdus nematophila strain from Steinernema carpocapsae collected in Moscow region demonstrates the differences in only 3 positions from typical X. nematophila from Western Europe. This 16Ssequence clusters together with those of X. nematophila from USA, Poland, Portugal, Jordan and Peru. Bootstrap support (maximum parsimony analysis) for this group was weak only. Three cultures of S. feltiae used to extract X. bovienii were isolated in reciprocally remote points (Central Europe, Armenia, Moscow region). Still 16S-sequences of obtained X. bovienii were identical. Pronounced similarity was found between 16S-sequences of X. szentirmaii, X. koppenhoeferi и X. japonica and that of Xenorhabdus from undescribed Steinernema sp. «Bush-Augusta» (MO, USA). The closest bacterial species is X. szentirmaii. The sequences of Steinernema sp. from Cameroon were clustering in some cladograms with X. miraniensis.