Chongming Island, a large island off the Shanghai Coast, is China's first and only endorsed eco-island. The Chinese central government and the Shanghai provincial government have placed high bets on making Chongming a world-class example of sustainable urbanization and involved the United Nations Environmental Programme (UNEP) for valuable knowledge transfer. However, to what extent is it feasible to preserve the green, open and natural character of the island given the enormous urbanization pressure Shanghai faces? In this contribution, the authors examine to what extent the lofty goals formulated in the various national, provincial and local plans are effectively implemented. They claim that existing assessments are useful, but rely too heavily on technocratic indicator systems to allow for insights regarding on the ground implementation. They analyse existing assessment studies on eco island development, but then develop a broader planning and policy oriented assessment matrix of their own which they apply in an independent field study. They find that the Shanghai and Chongming authorities are generally taking their eco island development task seriously through restricting urban development to certain locations, opening eco-parks, developing an integrated water system, and invest substantial resources into making it happen. However, a sustainable public transport system is still missing and at a few locations commercially attractive to real estate development villa parks and skyscrapers have emerged. By synthesizing data from existing evaluations with information retrieved following the format of their assessment matrix, an analysis of the eco island's implementation which connects more closely with the situation experienced on the ground has been generated.