A new ascaridoid nematode Mawsonascaris zhoui sp. nov. collected from the granulated guitarfish Glaucostegus granulatus (Cuvier) (Rajiformes: Rhinobatidae) in the Taiwan Strait (off Xiamen, Fujian Province, China) is described and illustrated in this paper. The new species can easily be distinguished from its congeners by the absence of an intestinal caecum, the presence of a single, median precloacal volcaniform papilla, a pair of paracloacal double papillae and 10โ11 precloacal papillae in the male. In addition, the paratypes of Raphidascaroides myliobatum Yin & Zhang, 1983 collected from the Japanese eagle ray Myliobatis tobijei Bleeker (Rajiformes: Myliobatidae) in the Taiwan Strait (off Chongwu, Fujian Province, China) were also re-examined and the morphology of the species reveals that it also belongs to the genus Mawsonascaris, as M. myliobatum (Yin & Zhang, 1983) comb. nov. An identification key to the species of Mawsonascaris is provided.