European flat oyster (Ostrea edulis) and Mediterranean mussel (Mytilus galloprovincialis) are one of the most commonly farmed bivalves in the Mediterranean. In addition to being a source of food to many organisms in the sea, bivalves' meat have high nutritional value and contributes also to human health. In order to conduct an analysis of the chemical composition and the composition of fatty acids, farmed bivalves O. edulis and M. galloprovincialis were sampled from the Novigrad Sea in the late autumn. Also, the aim was to determine the suitability of the Novigrad Sea for farmed organisms based on the obtained results. The chemical composition of bivalves was not constant, but it changed depending on different seasons and environmental factors associated with a particular period of year. The fat content measured in O. edulis was 1,76 g, while in M. galloprovincialis determined content was 1,02 g. After spawning, the lipid value was significantly reduced and the protein ratio increased. In the composition of oyster fatty acids, the highest percentage had palmitic fatty acid, which belongs to the group of saturated fatty acids. In mussels, on the other hand, results have shown that docosahexaenoic acid (DHA) from the omega-3 group, was the most represented. It has been determined that the percentage of unsaturated fatty acid in both bivalves makes up the largest share of total fatty acids, especially DHA found in phytoplankton. Temperature, salinity, concentration of dissolved oxygen and salt in the sea determined the growth of phytoplankton, and thus influenced the development and chemical composition of bivalves' meat, as well as the composition of fatty acids.