Buildings, infrastructure, and durable goods are essential for human activities. Understanding their relationship with socioeconomic development is crucial for optimizing resource allocation in urban settings, thereby enhancing efficiency and lessening environmental impact. This study delves into the urban material stock evolution in China's megacities, spanning 111 distinct end-use stocks. From 1978 to 2018, in-use stocks witnessed a substantial surge, increasing from a modest <350 Mt to an astounding 819–3130 Mt across cities—an average annual growth rate ranging from of 4.7 to 15.2 %. This growth was paralleled by improvements in stock productivity, associated with reductions in CO₂ emissions by 154–505 Mt and conservation of significant amounts of energy and food resources. As urbanization approaches the 80 % mark, a mere 1 % rise results in considerable increments of 13.5, 1.9, and 0.6 t in per capita stocks of buildings, infrastructure, and durable goods. Our results shed light on strategies for resource circulation, stock management, and sustainable urban future trajectories.