The desmid flora of Serbia has been surveyed during various periods. The first data on the distribution of desmids in Serbia date back to 1883 and from then on until 2009 altogether 630 different taxa were identified. Among 23 genera of desmids in all, the most diverse and most commonly found is Cosmarium (242 taxa or 38.4 of the total number of taxa). Taxa belonging to the genus Cosmarium grow in distinctly diverse habitats, from lowland rivers to high-mountain peat bogs. The present paper gives a survey of the major taxonomic and ecological characteristics of the Cosmarium taxa which have been identified in Serbia. The present studies regarding the distribution of Cosmarium taxa over the territory of Serbia, show that extremely rare, very rare and rare taxa comprise 96.3 of all recorded Cosmarium taxa. The species Cosmarium botrytis, C. laeve, C. meneghinii and C. subprotumidum appear widely distributed in the territory of Serbia. High-mountain peat bogs are characterized by the greatest diversity of the Cosmarium taxa.