This paper examines the application of sustainable tourism in protected areas on the example of the Nature Park Medvednica. Exceptional natural beauty and excellent preservation of environment is not only a prerequisite for potential tourism opportunities, but also a great responsibility because each overexploitation can lead to long-term harm in the environment. Sustainable tourism is imposed as an important element of modern tourism, which strictly controls the impact of tourism on the local environment. The balance between environmental, economic and socio-cultural components is therefore being mentioned in the programs and strategies for tourism development. Ecotourism is a form of sustainable tourism particularly applicable in the tourist development of protected natural areas. These natural units (national parks, nature parks, reserves, etc.) are gaining in popularity by attracting more and more tourists each year, and it is usually where ecotourism through education, volunteer activities and education about nature, helps to preserve and protect nature. Paper is divided into five sections. After introduction, the part will examine the impact that tourism has on environment and will introduce the idea of sustainable tourism development, with the involvement of local communities. The second part analyzes the concept of ecotourism, highlighting it's strengths and weaknesses and also gives an overview of ecotourism in Croatia. The third chapter deals with the touristic valorization of protected areas, which will be categorized according to international standards. The emphasis is on the role and importance of conserving protected areas, the need for monitoring and zoning, as well as the establishment of ecological networks. The fourth part discusses Nature Park Medvednica as a specific destination for sustainable tourism development, due to its natural and cultural values and rich biodiversity. A view on how the Park is managed is also shown. Methodology and research are displayed in the finale section as well as testing of research questions.