Abstract: The Rainy Zone of West China, which is located along the brim of the Sichuan Basin, ranges 50～70 km east to west and 400～450 km from north to south, with an area of 25 000 km 2 or 0.26% of the territory of China. This zone is well known for its beautiful landscapes, plentiful vegetation types, abundant resources and diversity of plants and animals. Unfortunately, the zone has not been recognized as a relatively isolated geographic unit and the biodiversity in the zone has not been studied. Through analyzing the extremely varying topography and landforms, special climate, unique vegetation types and species of plants and animals, and the populated areas in the zone, this paper briefly discusses the diversity of ecosystems and habitats of the zone. The rainy zone is a large scale and complicated ecotone that is a natural geographic unit, with a cloudy, wet climate as its main feature. It is a green barrier for ecological protection and development in western China, and a key region for biodiversity conservation and research in China. The results of this paper offer support for the suggestion that Rainy Zone of West China should be listed as a key ecological region of China and the world.