Though measuring and monitoring tourists' responsible behavior is considered as a key indicator of assuring Responsible Tourism (RT), it is highly ignored in most of the tourist destinations in Bangladesh. Hence, this research aims at investigating how responsibly the tourists behave in the context of an ecotourism destination, Saint Martin Island, Bangladesh. To address the research aim, this paper follows the quantitative research approach where both primary and secondary data are used. The study employed 18 RT behavioral traits under five broad themes to measure Responsible Tourist Behavior (RTB). The findings show that there exists a positive significant relationship between RTB and behavioral trait themes (environmental, economic, cultural, development and promotional, legal and ethical behavioral traits). It is also found that the tourists are very careless about using usual tourist path, local tourist guide, creating noise and wearing local dresses but they play a significant role for the promotion and development of the destination during their visit. Keywords: Responsible Tourism, Responsible Tourist Behavior, Ecotourism Destination, Saint Martin Island, Bangladesh