Protected areas hold a special position in terms of the sustainable socio-economic and tourism development of the planet. The International Union for Conservation of Nature has created a specific classifying system for cate­gorization of such areas depending on their nature-scientific and conservation value and significance. Except for preserving valuable biological species and their natural habitats, these areas could fulfill one more function. They can be integrated and contribute to the sustainable development of all spheres of socio-economic life of the com­munity. This paper sets the aim to determine to what extent and what categories of protected areas in Bulgaria could be integrated into the tourism sector of the country and to contribute that way to its sustainable development. Eco­tourism is considered as main tool to achieve this goal. Two concepts are laid upon its successful implementation. These are the concept for sustainable development and the one for development of alternative forms of tourism. The thesis that the concept for development of alternative forms of tourism is thought to compliment the one for development of sustainable tourism.