A middle Eocene through Oligocene calcareous nannofossil biochronology is established for the Southern Ocean through correlation of biostratigraphic datums with magnetostratigraphies at seven Ocean Drilling Program (ODP) sites in the Atlantic and Indian Ocean sectors of the Southern Ocean. Most of the middle and upper Eocene index fossils of the standard nannofossil zonations are present, but their ages are significantly different in the Southern Ocean from those in the mid or low latitudes. The standard zonations are generally not applicable for the uppermost Eocene through the Oligocene in the Southern Ocean due to the low abundance or absence of the zonal markers. Seven nannofossil datums that are not used in the standard zonations are calibrated with magnetostratigraphy, and these are quite useful for biostratigraphy in the Southern Ocean.