A light weight body structure development of the low floor bus was performed by the following three purposes. First, the development of the modularized structure of the low floor buses. Low floor buses are 4 types depending on the type of the fuel, which is CNG bus, HEV bus, electric bus, hydrogen electric bus. These buses have different body structures because the fuel systems are different in position and weight. So the modularity of the body structure is necessary to reduce the development cost. Second, the removal of the B-pillar diagonal reinforcement. In the low floor bus, diagonal reinforcement is installed near the B-pillar to support the roof on fuel system. This reinforcement needs to be removed because it inhibits the bus indoor living area and spoils the interior design freedom. Third, the weight reduction of the body structure. Because low floor bus is heavier than the normal city bus, the fuel efficiency of the low floor bus is lower than the normal city bus. So the weight reduction is essential for improving the fuel efficiency.