The late Pliocene is notable for the appearance of two new hominid genera as well as the first archaeological sites, generally attributed to the Oldowan Industrial Complex. However, the behavioral ecology of Oldowan hominids has been little explored, particularly at sites older than 2.0 Ma. Moreover, debates on Oldowan hominid foraging ecology and behavior have centered on data from only two regions, and often from single site levels. Here we describe the preliminary results of our investigation of Oldowan occurrences at Kanjera South. These occurrences preserve the oldest known traces of hominid activity in southwestern Kenya, and unlike most of the Oldowan sites in the 2.0-2.5 Ma time interval, artefacts are found in spatial association with a well-preserved fauna. In 1996 and 1997, this project initiated the first excavation program for Kanjera South. Magneto- and biostratigraphy indicate that deposition began approximately 2.2 Ma, substantially earlier than previously thought. At Excavation 1, artefacts were found in spatial association with a taxonomically diverse faunal assemblage in Beds KS-1 and KS-2. Excavation 2 yielded a partial hippopotamus axial skeleton with artefacts in KS-3. Cores from both sites were incidentally flaked and represent a Mode I lithic technology indistinguishable from the Oldowan. Approximately 15% of the artefacts were manufactured from non-local raw materials, indicating a flow of resources into the area. Stable isotopic analysis of KS-1 and KS-2 pedogenic carbonates suggests that the Excavation 1 assemblages formed in a relatively open (>75% C4 grass) habitat. The Excavation 1 and 2 faunas contain a high proportion of equids relative to Oldowan accumulations from Bed I Olduvai Gorge, Tanzania. Beds KS-1 and KS-2 thus preserve traces of Oldowan hominid activities in a more open setting than has been previously documented.