This paper presents excavation results from Nyabusora, northern Tanzania, conducted by M. Posnansky and W.W. Bishop (1959) and M. Posnansky (1961). Only preliminary reports have previously been published. It synthesises the site’s history, incorporating previously unpublished analyses and information from Posnansky’s original field notes, and presents new 2014 field survey results and new archival research. Nyabusora holds particular significance as the only Early to Middle Stone Age (ESA/MSA) site in the region to have yielded both lithic and faunal remains, which gain new relevance in light of recent developments in ESA/MSA archaeology in eastern Africa. Nyabusora’s ‘Sangoan’ lithic assemblage is now largely decontextualised and associated finds have been lost, so this study presents the only available lithic and faunal analyses, alongside interpretations of the stratigraphic sequence and site. Such stratified assemblages are exceptionally rare and are generally attributed to the Middle Pleistocene. This research enhances understanding of Plio-Pleistocene landscape evolution in the Kagera River and western Lake Victoria-Nyanza Basin. It contributes important new data on ESA/MSA lithic variability and, via ongoing investigations by Basell within the Kagera catchment, offers huge potential for clarifying Middle Pleistocene palaeoenvironments.