This paper examines how local knowledge is employed in environmental adult education in a community-based ecotourism project in an island community in southern Thailand. The study is based on field research and analysis of project websites, media reports and documents. Situated at the intersection of global tourism and a local Thai-Malay Muslim fishing community, the ecotourism project functions as an alternative tourism development model challenging dominant practices of mass tourism. In the project, tourists stay as guests in local homes, and learn firsthand from family and community ecotourism guides. The informal ecotourism "curriculum" for tourists centres on local knowledge of tidal and marine ecosystems, environmental conservation efforts, local culture, and traditional livelihood activities. Tourists learn experientially to understand and appreciate this local knowledge, and in the process, contribute to the sustenance of the community, to the preservation of culture, and to the conservation of the marine resources upon which the community depends. Members of the ecotourism project, for their part, have engaged in a wide range of adult learning over the project's lifespan. This learning includes skills and knowledge in ecotourism management, environmental conservation, cross-cultural exchange and political activism. Although the advent of mass tourism on the island now threatens to overwhelm the local community, the capacity for environmental adult education, adult learning and political activism built up over many years by members of the ecotourism project will likely help to moderate, if not control, the deleterious effects of future commercial development. (Contains 2 figures and 3 notes.)