We proposed a biozonation of the Middle and Upper part of the Sarmatian Stage, based on siliceous microfossils (silicoflagellates Distephanopsis soljani–Distephanopsis slavnicii Zone and diatoms Anaulus simplex–Coscinodiscus doljensis Zone). The new silicoflagellate and diatom zones have been correlated with other already proposed zonations for the Paratethys Sea and other marine realms. 46 diatom and 3 silicoflagellate taxa have been determined, that were hitherto not known from the Croatian part of the Sarmatian Paratethys. The boundary between Middle and Upper Sarmatian is supposed to be indicated by the change within the diatom assemblages and by the complete disapperance of silicoflagellates. Tuffitic particles, occurring at the boundary, could also be used as a marker. Likewise a drastic decrease of macrofaunal (molluscs) and microfaunal (foraminifers, ostracods) content is observed. The reason for changes in species assemblages could be in gradual disconnections between Central Paratethys and other marine realms (Eastern Paratethys, links through the Mediterranean to the Atlantic and towards the Indopacific) providing more near shore influence and less saline environment during the Late Sarmatian.