A survey of stag beetle (Lucanidae)-associated nematodes was conducted in Japan to construct a preliminary species inventory and to obtain their molecular profiles as a first step for elucidating their host fidelity and ecological roles. Eight species of stag beetles (94 individuals in total), Dorcus rubrofemoratus, D. montivagus, D. striatipennis, D. rectus, D. titanus, Prismognathus angularis, Prosopocoilus inclinatus, and Lucanus maculifemoratus were collected from 12 localities in Japan, dissected and examined for nematode associates. Isolated nematodes were used to attempt the establishment of voucher cultures. Successfully cultured nematodes were observed under a light microscope for morphological identification at genus or species level, and were sequenced for their near full length SSU and D2/D3 LSU. All investigated lucanid individuals harbored at least one species of nematode, and eight species (Bursaphelenchus sp., Koerneria luziae, K. lucani, Pristionchus cf. pacificus, Pristionchus sp., Pseudodiplogasteroides composites, Pseudodiplogasteroides sp., and Rhabditidoides sp.: 40 populations of nematodes in total), were successfully cultured from the insects. Within these eight species, four species were considered to predominate and had low carrier specificity and wide distribution, i.e., K. luziae, P. composites, Pristionchus sp. and Rhabditidoides sp. were isolated from various species of beetles and from several different localities, and K. luziae, K. lucani, and P. composites have been previously described from native lucanids in Germany. Considering the recent world-wide trade of living insects, especially lucanids as pets, we suggest the use of caution to prevent the invasion of their associated nematodes and other associated organisms.