This paper reports the results of field studies on the Late Miocene Baccinello-Cinigiano Basin (Southern Tuscany, Italy). Sedimentological and paleontological analysis of the fossil vertebrate-bearing deposits provided a detailed picture of the basin fill evolution. The deposits consist of gravels, sands and clays formed in several environments ranging from alluvial to fluvial and lacustrine. The occurrence of four distinct mammal assemblages (V0-V3) found in specific stratigraphic intervals allowed a fine local biochronologic calibration of the basin fill to be defined. The Ar/Ar dating of a primary tephra to about 7.5 Ma provides a well-constrained reference for the assessment of the sedimentary and paleobiogeographic evolution of the basin and surrounding areas. The main products of this study are a geological map, scale 1:25.000, showing two upper Miocene synthems bearing several lithofacies associations, a better stratigraphic-depositional understanding of the basin evolution, and a qualitative evaluation of the tectonic control on the basin dynamic expressed by changes of accommodation space and routes for sediment supply. The mammal assemblages V0-V3 suggest that some events which affected the basin from the mid-late Tortonian to the late Messinian have wider tectono-sedimentary implications at least in an area between the south-western Alps (i.e. the Tertiary Piedmont Basin) and the Northern Apennines.