The fossil monkey remains of the Mount Galili Formation, southern Afar depression (Somali Region), Ethiopia, offer a rare opportunity to study the taxonomic shift in Early Pliocene cercopithecoids at a single site. Based on biostratigraphic correlation of suids and elephantoids as well as radiometric results, the fossiliferous sediments at Galili are estimated to cover the time span between about 4.5 and 3.5 million years ago. More than 350 cercopithecoid specimens (about 16 percent of the total faunal remains) representing conceivably seven different taxa were collected from different stratigraphic horizons. Though in total colobines make up less than one fourth of the primate assemblage at Galili, they account for almost fifty percent in sediments of the lower Mount Galili Formation. However, the colobines from these sediments do not measure up in quantity to those from the contemporaneous site of Aramis, Middle Awash - indicating a less closed woodland habitat at Galili. This is consistent with the comparatively higher percentage of Reduncini at the latter site. While in the oldest sediments at Galili fossils of colobine monkeys and Pliopapio predominate, the younger sediments accommodate few colobine fossils, but primarily fossils of ?Parapapio and early forms of Theropithecus.