This paper examines the sustainability of ecotourism on Yao Noi Island based on nine indicators covering environmental, economic and sociocultural dimensions. Required data were collected through a survey of 178 households using a structured questionnaire and participatory appraisal methods. The findings revealed a majority of local people across income brackets benefited from the employment opportunities generated by ecotourism. However, the condition of the natural and environmental resources that served as a foundation of ecotourism was gradually degrading. Regarding social sustainability, locals had taken opportunities to strengthen their capability to promote ecotourism. However, social vulnerability has resulted from increased land grabbing and investment by outsiders, and encroachment by external cultures into the unique Muslim culture. It suggests ecotourism on Yao Noi Island could be sustainable if appropriate interventions were made to ensure the effective conservation of environmental and natural resources and to protect the landownership of private property by local people.