Abstract Crassostrea oysters present planktonic/planktotrophic larval development. Thus, it is essential knowing larvae distribution patterns in estuarine environments presenting oyster farms and spat collection. The aim of the current research is to investigate the spatio-temporal distribution of oyster larvae in Guaratuba Bay (Paraná State - Brazil) based on monthly samplings conducted with a plankton net (50 cm diameter and 225 µm mesh size) from June 2003 to June 2004 in three different points (Point I - bay´s entrance; Point II - cultivation park; Point III - median sector of the bay). Plankton samples were preserved in 4% buffered formaldehyde. They were concentrated and quantified in the laboratory. The total number of larvae in the sample from each net was counted and corrected to a standard larvae/m3 collection tow. Data about sea water temperature, salinity, transparency and pluviosity were also collected. Based on results about the spatial distribution of larvae, mean density was 33.30 ±42.73 larvae/m³ in Point I; 17.84 ±16.88 larvae/m³ in Point II and 55.53 ±78.31 larvae/m³ in Point III, during the studied period. Spring and Summer were the seasons recording the most expressive mean number of larvae; the largest concentration of them was found in Point III, in the middle section of the bay.