This study analysed mountain guides' representations of environmental responsibility and explored the paradox that these professionals face: using nature as a source of income while trying to preserve it. The study was mainly guided by the philosophical literature on this topic and made use of the concepts of sustainable development and nature. This exploratory work therefore contributes to the new field of environmental social psychology. Semi-structured interviews were conducted and the qualitative analysis showed that mountain guides have a very sensitive and contemplative approach to moral aspects of our relationship with nature, which they try to transmit to their clients. They believe that this is a way to educate people about sustainable development, but this term emerged as quite vague for them, and they expressed the opinion that it might hide other concerns, such as to make translating it into moral conduct a difficult matter and to compromise their identity as moral actors. (Contains 3 tables and 6 notes.)