In recent years, tourism, especially in terms of marine tourism, has played an important role in the economic development of every country. Profits from tourism activities contribute a significant portion to their total annual incomes. Many countries have put great efforts into developing their marine tourism industries to attract tourists from all over the world. This has created fierce competition among countries which have similar geographic and natural conditions in the same region. In this study, the importance of factors that make a competitive marine tourism industry of major countries in Southeast Asia such as Vietnam, Thailand, Singapore and Malaysia were identified and evaluated by using AHP (Analytic Hierarchy Process). Questionnaires were given to candidates who are working in Southeast Asia or having experiences in traveling to the area to determine the weight of these factors and the preferred country to travel. The results show that Singapore was the most preferred tourism country in Southeast Asia and Quality was the most important factor to be concerned when the tourists consider traveling to the area. Moreover, the strengths and weaknesses of each country have been indicated and provided as useful information for tourists who are planning to visit the Southeast Asia region.