The promotion of tourism has been considered to be a key strategy in reducing people's dependence on marine resources and for creating alternative livelihoods for the communities living in Marine Protected Areas (MPAs). This paper studies the determinants for the decision of participation in tourism-related activities and examines whether tourism could be regarded as an alternative livelihood for the local people living in the MPAs. The propensity score matching approach is employed and a case study of Nha Trang Bay MPA is used for analysis with data from 140 locals. The results show that the tourism industry in the MPAs does not secure a better income for the local people if they stop their traditional livelihoods and enter the tourism industry. In other words, tourism should not be viewed in isolation with other existing income generating activities. Furthermore, low education, long distances between home and tourism destinations, and the pressure of supporting the whole family are the primary rationales preventing local people living in MPAs from participating in tourism industry. This paper discusses implications for the management of MPAs in developing countries, where tourism is used as the main strategy to diversify the local people out of traditional fishing or aquaculture. •MPAs are recognized as a conservation tool for high marine biodiversity.•Tourism livelihood is expected to replace traditional fishing and aquaculture in MPAs.•Tourism can act as a supplemental income rather than an alternative livelihood.•Low education, poor transportation, and financial pressure are the rationales for not participating in tourism.