Urban ecotourism is defined as the travel and exploration activities which take place in and around a city that provides visitors and residents with a greater appreciation and conservation of the cities' natural and cultural resources. Planning ecotourism activities in the urban context is a multidimensional task which requires consideration of environmental, social, and economic issues. The purpose of this study is to propose a fuzzy multicriteria approach for the selection of the most appropriate site(s) for promoting ecotourism activities in urban areas using a modified PROMETHEE methodology. In the suggested methodology, the importance weights of the evaluation criteria are determined by a fuzzy pair-wise comparisons procedure. The fuzzy sets theory is a good tool for dealing with subjective and implicit human judgments. PROMETHEE III outranking methodology is used to make a prioritization among seven different districts of Istanbul. Finally, a sensitivity analysis is conducted to test the robustness of the results.