The theme of this master thesis is the sustainable development of protected areas. A special review in the work refers to the protected areas in Croatia, with particular reference to the Krka National Park. Protected areas in the world are becoming more popular tourist attractions, and their protection and adequate exploitation are of extremely great importance. This thesis aims to show the importance and significance of sustainable development in protected areas. The thesis begins with an overview of the concept, definition and objectives of sustainable development. Furthermore, thesis analyzes the sustainable development of protected areas in the world and the European Union, and also the categorization of protected areas in six main categories according to the IUCN. Part of the thesis presents sustainable development of tourism in Croatian protected areas and it is presented development of tourism in national parks, which increases every year. Although growth in visits has a positive effect on many aspects, Krka National Park is facing a few problems, especially during the season when it is reflected huge impact on the environment. In response to exceeding the reception capacity it is presented Management plan as an instrument to improve the sustainable development of Krka National Park.