lowermost division of Oligocene (Oligocene Epoch) rocks, representing all rocks deposited worldwide during the Rupelian Age (33.9 million to 28.4 million years ago) of the Paleogene Period (65.5 million to 23 million years ago). It is named for exposures studied along the Rupel, a tributary of the Scheldt River in Belgium.

The Global Stratotype Section and Point (GSSP) defining the lower boundary of this stage, ratified by the International Commission on Stratigraphy (ICS) in 1992, is located in the Massignano section, which lies in a quarry about 10 km (6 miles) southeast of Ancona, Italy. This lower boundary matches the extinction zone of the foraminiferan (pseudopod-using unicellular organism protected by a test or shell) genera Hantkenina and Cribrohantkenina. The upper boundary is located near the extinction level of the foraminiferan Chiloguembelina. The Rupelian Stage overlies the Priabonian Stage and underlies the Chattian Stage.