Ecological knowledge and destination image are important drivers of ecotourism. Although previous studies have explored the antecedents of ecotourism intentions, our understanding of the factors driving demand for ecotourism is still limited. This study explored factors that affect ecotourism intention. Ecotourism knowledge and destination image were evaluated from the perspective of the theory of planned behavior. In total, 441 valid questionnaires (in paper and electronic format) were obtained and analyzed using a structural equation model. We developed an extended theoretical model of planned behavior. The results showed that ecological knowledge, attitude, and perceived behavioral control had a significant impact on ecotourism intention. Destination image directly affected attitudes toward ecotourism. Ecotourism attitude and subjective norms mediated the relationship between ecotourism knowledge and ecotourism intention. This study extended the theory of planned behavior to analyze ecotourism intention according to ecotourism knowledge and destination image. The findings of this study enrich the literature on tourism and consumer behavior, and also have practical implications for ecotourism operators aiming to design experiences for tourists, as well as for government and non-profit organizations attempting to promote ecotourism.