This dataset provides planktonic foraminiferal assemblage data from the marine sediment core GeoB5901-2 (Gulf of Cadiz). Planktonic foraminiferal species are presented in percentages of total counts in relation to core depth. The dataset has been accomplished in 2017/2018 and form the basis of SIMMAX-derived seasonal sea surface temperature reconstructions (doi:10.1594/PANGAEA.899720). AMS dates for the core can be found at doi:10.1594/PANGAEA.912670. In order to count planktonic foraminiferal specimens approximately 10 cm³ of sediment sample has been washed over a 63 µm sieve and was subsequently dried at 40 °C. The samples were then dry-sieved for larger fractions. Foraminifera have been counted under the microscope from the > 150 µm fraction, which previously has been split into aliquots of at least 300 specimens using a Kiel dry sample splitter.