Holocene ostracods from a core obtained in the Itapeva Lake, Rio Grande do Sul coastal plain, are studied in this paper. Twenty-six species belonging to 22 genera and 13 families were registered in nine samples analyzed, two of them new: Cytherella eros sp. nov. and Loxoconcha itapevensis sp. nov. The taxonomic composition of the assemblages varies along the core, being Cyprideis multidentataHartmann the most abundant and frequent species (273 specimens), followed by Cytheretta punctata Sanguinetti (56 specimens) and L.itapevensis sp. nov. (51 specimens). Variation in richness and diversity observed along the core probably results from sedimentary and hydrological changes during the evolution of the Itapeva Lake. The results obtained in this work reinforce the importance of ostracods in the study of coastal paleoenvironments. Keywords: barrier-lagoon system, biostratinomy, micropaleontology, Quaternary.