Eight species among six genera of bopyrid isopods (representing the subfamilies Pseudioninae and Ioninae) infesting thalassinideans from China are reported. Of these, four species are new to science: Gyge fujianensis n. sp., Progebiophilus elongatus n. sp., Upogebione bidigitatus n. sp., and Procepon liuruiyui n. sp., infesting Upogebia major (de Haan), Nihonotrypaea japonica Ortmann, Upogebia carinicauda (Stimpson), and Austinogebia wuhsienweni (Yu). One species, Ione cornuta Bate, 1864, is recorded for the first time from Chinese waters and from a new host. Pseudione longicauda Shiino, 1937, Gyge ovalis (Shiino, 1939), and Progebiophilus sinicus Markham, 1982, previously known from Hong Kong or Taiwan, are recorded for the first time from mainland China, extending their range north.