Abstract: During the Jurassic–Cretaceous (J–K) transition, global ecosystems underwent profound changes. Studies on biodiversity during this period indicate that approximately 20% of marine species went extinct in shallow-sea environments, while on land, crocodyliform diversity declined by 55%–75%, and tetrapods and pterosaurs experienced a 75%–80% reduction in diversity. Overall, larger-bodied taxa were disproportionately affected. However, the evolutionary trajectory of terrestrial ecological diversity during this pivotal transition remains poorly constrained. In Asia, stratigraphic successions spanning the Late Jurassic to Early Cretaceous are well developed and have yielded abundant vertebrate fossils, making the region a key area for reconstructing the evolutionary history of terrestrial ecological diversity across the J–K transition. In this study, we compiled occurrence data of vertebrate fossils from the Late Jurassic to Early Cretaceous of Asia and integrated species-level ecological traits for analysis. Ecological classification was established based on habitat, diet, and body size, with body size data measured to refine trait differentiation. Resampling methods were applied to correct for sampling bias and uneven sample sizes. The results show that large-bodied saurischian dinosaurs (by approximately 50%–80%), turtles (about 40%–50%), and mammals (about 60%–70%) experienced marked declines in diversity across the J–K boundary, whereas freshwater fishes and some other reptilian groups were less affected. Analyses of ecospace structure reveal substantial adjustments in both species diversity and functional structure within Asian terrestrial ecosystems during the J–K transition. Furthermore, responses to environmental factors varied markedly among clades: overall, vegetation changes appear to have promoted increases in aquatic diversity, whereas climatic warming and increasing aridity exerted strong suppressive effects on the diversity of terrestrial groups.