Ecotourism is a nature- and culture-based type of tourism. Ecotourists demand more environmentally aimed tourism experiences. Ecotourism practices should result in a non-consumptive use of natural and cultural resources. However, while ecotourism activities contribute to the visited area by generating economic benefits and educational opportunities, they may affect some resources negatively. For this reason, ecotourism must be managed by sustainability principles. Resource managers have to apply ecological, economic, social and cultural criteria when choosing their alternative ecotourism activities regarding sustainability. Inappropriate activities may damage cultural and natural elements of visited areas. To consider all dimensions of the ecotourism, planners should use multi-criteria decision-making techniques and participatory approaches to take into account social, economic and environmental dimensions of ecotourism. The techniques designed in this paper consider decision makers, the public, and sector experts' preferences in choosing alternative activities of ecotourism planning. They were evaluated using ELECTRE I (Elimination and Choice Expressing Reality), ELECTRE III and AHP (Analytic Hierarchy Process) techniques to address the same decisionmaking problems in the Cehennemdere Valley in the Mersin province. By using the AHP, ELECTRE I and III models, the preferences of stakeholders could be clarified, the ranks of the activities could be generated concerning multiple criteria, and the results of these techniques could be compared with respect to using them for sustainable ecotourism planning. This research demonstrates that the results of different decision techniques may differ when applied to the same problem. © 2011 Academic Journals.