Dugi otok is located in Zadar Archipelago and it is one of the outer island, what makes it a natural barrier towards the open sea. Geologically, carbonate rocks are prevailing. Dugi otok is surprisingly rich in speleological objects, which are mostly scientifically neglected. Out of 57 caves and pits that are mentioned in the literature, only cave Vlakno and Strašna pe´c have so far been systematically researched. This thesis consists of a short overview of the most important research of the speleological objects of the island Dugi otok and of results of the research performed by Biology Students Association - BIUS with the mentoring of Croatian Biospeleological Society - HBSD. The most significant speleological results are the topografical schemes of four speleological object: Jama na Jamnjaku, Jama s vodom kraj sela Luka, Cˇ elinjak and Podslotinjak. Biologically, the most important results of this research are collecting of the specimens that have been used for the description of the new species Alpioniscus drazinai Bedek, Gottstein & Taiti, 2019 as well as collecting of the specimens of the new species of family Trichopolydesmidae (Myriapoda: Diplopoda). There are still a lot of objects on the Dugi otok island that need to be surveyed both speleologically and biosoeleogically. Further research should be done on the Dugi otok island during which it is to be expected to discover more troglobiontic organisms.