This paper presents the implementation of an hybrid series Bus with a gas turbine, as thermal engine. The hybridization methodology for transforming city buses, substituting the original gasoline/diesel engine with a micro gas turbine device (intended as range extender), into a series hybrid vehicle has investigated and its feasibility analyzed. The study was conducted by the university of Rome “Sapienza” in collaboration with several enterprises. The idea is to design a hybrid power train that can be installed in a typical city bus, which means that all systems and components will be influenced by the limited space available. In this paper the details of the mechanical and electrical realization of the power train will be discussed. The hybrid system also includes consideration on the battery pack and the vehicle management logic. The proposed solution obtains a reduction in fuel consumption higher than 20%, in comparison with normal commercial fleet