Geothermal surface exploration in SW Tanzania in the frame of the GEOTHERM programme in 2006-2009 allowed to evidence and characterizes the Ngozi Songwe geothermal system in the area of Mbeya, as part of the Rungwe Volcanic Province. This paper presents the geological and sismotectonic aspects of the geothermal system, including the distribution of seismic epicentres, Quaternary volcanic vents, and thermal springs (hot/cold) and gas vents (CO2). The geothermal system is closely related to the Ngozi volcanic system and is associated to large travertine deposits, that started to be active at least 36 Ka ago U-Th dating on Songwe Travertine. The Late Quaternary stress field and related deformation define the structural architecture of the volcanic system and exert a strong influence on the thermal waters which are circulating trough the active fault network. The strong altitude gradient drives efficient and distant transfer of the fluids from the Ngozi volcano recharge area, trough the geothermal reservoir located between the Ngozi crater and Mbeya town, towards the discharge areas in the Songwe valley.