The small modern insect order Grylloblattida has an abundant fossil record during the Late Palaeozoic and the Mesozoicirca. The relationships between these fossil taxa and the modern grylloblattids remain unclear because most of them are based on isolated wings or have poorly preserved body features. Modern grylloblattids are wingless insects. The new grylloblattid family Plesioblattogryllidae fam. nov. is erected for the new genus and species Plesioblattogryllus magnificus gen. nov., sp. nov., from the Middle Jurassic of north-eastern China. The well-preserved specimen provides further evidence that could support its close relationships with the modern grylloblattids: (1) several very similar head structures, e.g. developed laciniae with inner row of setae, maxillary palps segmented into five, labial palps segmented into three, large labrum, and morphology of antenna; (2) paired eoplantulae on tarsomeres 1–4; (3) long ovipositor and large eggs comparable with those of modern taxa. The new genus has strongly developed mandibles with sharp pointed apical teeth and strong marginal teeth, and strong hook-like fore claws with basal teeth, suggesting it was carnivorous. The major differences between the extinct and extant Grylloblattida, such as the lack of wings, the eyes and ocelli either degenerated or absent, and the thorax degenerated in the modern forms, are probably related to their adaptation to their life under rocks and rock-crawler habits. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 152, 17–24.