Croatia has well-indented coast and numerous islands and it is challenging to connect 48 permanently inhibited islands and at the same time respond to the requests of the population of the islands and their tourists in the maritime passenger transhipment. Although the liner passenger shipping has been established for series of years, it nevertheless requires a systematic approach to future development. Quite a number of scientific and technical papers have been written about the elements and the factors of the RO-RO liner passenger shipping significance. In this article authors examine the importance and role of the liner passenger shipping in connecting the islands with its mainland. This paper aims to evaluate the existing state of the port capacities for accommodating the RO-RO ships in order to modernize it and to emphasize the need for the improvement of the liner passenger shipping. Further in the paper, the maritime traffic of passengers and vehicles in the permanent line connection of the island and the mainland and the islands with each other in the Republic of Croatia. Particular attention has been paid to the level of development of the existing infrastructure for the accommodation of the RO-RO ships in the most significant Croatian ports. RO-RO passenger shipping is one of the key factors of the development of the Croatian islands. Authors point out the need to strengthen the role of the RO–RO passenger shipping as important part of maritime sector in the development and competitiveness of the Republic of Croatia through initiatives of sustainable growth of economic activities on islands and in the coastal area. The RO-RO passengers traffic simulations system would result in better insight into the possibilities for a more flexible connection of islands and mainland.