During a survey of the biodiversity of entomopathogenic nematodes in Ukraine, a population of Steinernema arenarium, strain Ch, was recovered in the sensitive Chornobyl Exclusion Zone. In the present work, this strain was morphologically and molecularly characterised using light microscopy and the sequences of the ITS and D2–D3 region of the 28S rDNA. In addition, we sequenced the ITS and D2–D3 regions of four populations of S. arenarium from a laboratory collection. Phylogenetic analyses were performed and the phylogenetic structure and geographic distribution of S. arenarium are discussed.