The Mali Ston Bay (Southern Adriatic) is one of few areas where Mediterranean mussel reach the market size (60 mm) in two years. Scientific attempts at describing the relationship between mussel growth rate and food supply in the Mali Ston Bay have not been done in details yet. The purpose of this study was to examine the effects of phytoplankton and microzooplankton population densities and species compossition on the growth of the mussel Mytilus galloprovincialis. The mussels shell growth rate and flesh dry weight were investigated monthly at Bistrina Station (8 m maximum depth) from April 1984 to May 1985. In this study, the growth rate was evaluated at 1, 3 and 6 meters depth. Hydrography, nutrient concentrations, phytoplankton and microzooplankton were analysed monthly at the depth intervals of 1 meter. The best mussel shell growth rate and flesh dry weight were recorded in June-July, when an intensive development of microphytoplankton and nanophytoplankton population densities occured. Although according to statistical analysis, no significant difference in shell growth rates parameters existed between depths, highest average monthly shell growth rate was at 6 m depth for length and height, and at 3 meters for width. A qualitative composition of microphytoplankton species in the sea water as well as fecal pellets were similar. On the basis of the analysis of the fecal pellets mussels ingested diatoms, dinoflagellates, tintinnines, nauplii, small copepods and Bivalvia larvae.