Technical Abstract: Chroniodiplogaster formosiana sp. n. (Rhabditida: Diplogasteridae) is described from a population of Odontotermes formosanus Shiraki (Isoptera:Termitidae) collected from dead (unidentified) wood at Dinghu Park, China. Characters of C. formosiana which separate it from C. aerivora (Cobb) are a longer tail, the presence of 4 micropapillae (quadriform condition) and the adjacent position of the second and third macropapillae on the male tail. The diplogasterid, Pristionchus uniformis Fedorko & Stanuszek, which is transferred to Chroniodiplogaster, can be distinguished from both C. formosiana and C. aerivora by the position of its excretory pore. Mortality of Formosan termites by C. formosiana occurred after developing stages had established themselves in the host’s alimentary tract. Eventually the nematodes would break through the gut wall and cause a fatal septicemia. Variable results in experimental infection trials suggests that some still unknown factor or factors are important in determining termite susceptibility to the nematodes. Further studies are necessary to better define these factors before C. formosiana can be considered as a biological control agent of the Formosan termite.