The Thai Pollution Control Department (PCD) decided in 1994 to pursue the development of a 12-meter hybrid electric bus that would operate successfully in Bangkok environment. The development work began in January 1997. The hybrid-electric bus design concepts are discussed. The hybrid system components and their functions were presented in this paper. The hybrid-electric chassis was first tested in a racetrack near Atlanta in July 1998. Test results were compared to the design data. The hybrid-electric chassis was shipped from Georgia to Bangkok in December 1998. “Real World” testing began in June 1999. The test program was successfully concluded in December 1999. Results were reviewed and problems encountered during the testing as well as appropriate solutions were discussed.