The aim of this year-round research was to determine macrozoobenthos taxa inhabiting Mrtvo more on Lokrum Island. There were 25 species noted conducting visual census method: 3 species of class Anthozoa, 6 species of class Gastropoda, 1 species of class Bivalvia, 2 species of phylum Polychaeta, 8 species of class Crustacea, 1 species of class Echinoidea, 3 species of class Holothuroidea and one species of class Asteroidea. Average abudance of every species was estimated visually. During this research abiotic factors (temperature, salinity, dissolved oxygen concentration) were measured and concentrations of TAN, NO3-N, NO2-N and PO4-N (mg/dm3) were determined. More rapid changes in temperature and salinity were asserted in Mrtvo more in comparison to the surrounding sea. Dissolved oxygen concentrations were >4 mg/dm3, except during the summer months of July and August when concentrations droped to 2.8 and 2.9 mg/dm3 respectively. TAN, NO3-N, NO2-N and PO4-N concentrations were within normal parameters. Morphometric characteristics (height and width) of the most abudant mediolitoral species, marine snails Phorcus turbinatus and Cerithium lividulum were measured. Using linear regression analysis a positive allometric growth for both species was determined. Mean height and width were 13.57 and 14.52 mm, respectively for Phorcus turbinatus and for Cerithium lividulum 15.52 and 5.57 mm, respectively.