Authors conducted a sereis of studies on strength and behaviour of hybrid steel girders in order to obtain the backgound data which should be refered to establish the design method of hybrid steel girders numerically and experimentally. The current paper is aimed to represent the pricipal results of the experimental tests on hybrid steel girders. For the experimental tests, three test models were provided. The first and the second models were provided to investigate the fundamental behaviour and the effects of the longitudinal stiffener. In the third model, stiffening behaviours and effects of web plate by the transverse stiffeners at an intermediate support of continuous hybrid girder were examined. The first model was collapsed by the shear buckling of the web plate, and the second model is collapsed by the vertical buckling of the top flange. The third model shows the torsional buckling alike behaviour in the transverse stiffeners at an intermediate support.