Understanding the determinant attributes that affect the tourism attractiveness of National Parks is a strategic planning tool for protected areas. This exploratory study assessed the relative importance of various internal and external park characteristics on visitation numbers in Brazil. Data were collected from several sources: 28 park managers, internal park documents, government databases and various websites. The study used correlation and regression analysis. Results demonstrated that tourism attractiveness in the national parks can be predicted through reputation, recreation facilities, attractions in the region and population density. Results show that both internal park attributes and external setting characteristics are considered by visitors. The results have practical utility and can be used to improve investments efficacy among the parks that already receive visitors, as well as serve to evaluate the tourism attractiveness for new parks. Also, findings are useful for the communities and small businesses located in the adjacent areas, since adequate prediction of visitor demand provides support for tourism activities.