The marketing plan is one of the most important tools of marketing and instructs the entire company on the methods and activities that will be carried out in order to achieve the set marketing goals. A marketing plan is not only used to market the products and services of a company, but it is also used by state agencies to develop tourism in certain regions of the country. As one of the important aspects of marketing planning, we can single out research, so for the purposes of writing this master’s thesis, a quantitative research was conducted through an online form on satisfaction with the offers of the Kopački rit Nature Park and the regional area of Baranja. The theme of the thesis is elaborated through seven chapters. From the introduction and review of the literature, which includes the theory of the marketing plan, marketing in tourism and sustainable tourism, and the overview of the offers of the Kopački rit Nature Park, to the purpose, goal and problem of the research, elaboration of the results obtained from the research, discussion and conclusion. As a country where tourism is one of the main industries, it is evident that continental tourism during the summer (especially in Eastern Croatia) can hardly be compared to coastal tourism. The untouched potential of the Baranje region can be part of the key activities that will encourage and demonstrate the real results of decentralization and improvement of regional policy. The research participants recognized Baranja as an attractive area with its long history and gastro-ethnic offer, and would recommend it to their acquaintances. Preservation of nature together with sustainable marketing in tourism is a difficult job, but one that needs to be done well for the potential economic and social prosperity of the Baranja region, through which the rich history, identity and tradition of Baranja will remain preserved, and on the other hand attract foreign and domestic tourists and investors.