The purpose of this study was to identify the ostracod assemblage from a 43 m thick section of the Bizeljsko Formation, which constitutes the middle part of the Upper Miocene Posavje Group. The succession comprises sandstone, siltstone, and marlstone, deposited in a delta front environment. The determined ostracods belong to the families Cyprididae, Cytheridae, Darwinulidae, and Loxoconchidae. In total, 30 species were identified. Additionally, 8 morphotypes were determined at the genus level. The most common genera are Candona, Hemicytheria, and Cyprideis. The assemblage belongs to the Caspiocypris labiata subzone from the upper Pannonian. The ostracod assemblage from the Krško Basin is similar in species composition to Pannonian ostracod assemblages from Croatia and Serbia.