With the construction of a nautical tourism port in the Republic of Croatia its concessionaire, except the right to economically exploit the port he built, in accordance with the decision and contract on concession, has no other rights on the port and objects he built. Everything incorporated, later added or in any way permanently attached to maritime domain will remain its part, consequently its value will be increased. The aim of this paper is to determine in which cases the concessionaire who invested in maritime domain in the Republic of Croatia, and in that way increased its value has right to compensation for the investments he made. Although Maritime Domain and Seaports Act (MDSA) and Concession Act (CA) prescribe a whole series of reasons for termination of concession, the paper analyses exclusively the issue of valorisation of investments in case of its termination by expiration of time on which it is granted. Special attention will be devoted to issues of extension of concession (including its automatic renewal) right to priority concession, financial compensation which will be assigned by application of institute of gains without legal foundation, compensation of necessary and useful expenses which were not foreseen in the documentation on concession, as possible forms of reimbursement of that what the concessionaire has invested and what exceeds the amounts of resources anticipated with the decision and contract on concession. In relation to that matter, the issue of applicable national legal rules is particularly analysed, respectively the relation between CA and MDSA. We also investigate the influence of rules of the European Union on award of concession contracts and services in the internal market, respectively Directive 2014/23/EU and Directive 2006/123/EC on the interpretation and application of national rules. Judicial practice of the Court of Justice of the European Union which refers to interpretation of the relevant provisions of these Directives is analysed. Further, it is pointed to some solutions and doubts that emerged in comparative laws in relation to issues of awarding and extension of concession. Finally, solutions with respect to possibilities of valorization of the concessionaire’s investment in nautical tourism ports in the Republic of Croatia de lege ferenda are submitted.