Recently, the high tension steel with the yield stress of 800 kN/mm 2 was developed, and the loading test of the structural members with this steel has been confirmed. It is shown that the ratio between ultimate strength and yield strength is almost unity, so that the members with this steel have quite small ductility. When rigid moment resisting frames with high tension steel are subjected to seismic force, the fracture at the ends of beam may occur and it causes the strength of frames to decrease. On the other hand, the semi-rigid moment resisting frames without diaphragm with high tension steel can absorb the seismic energy at the beam-to-column connections due to its plate bending deformation. This study performs cycle loading experiments to high tension steel part frames, and compares the initial rigidity and the yield strength of part frames without diaphragm with that of part frames with diaphragm. In addition, these experimental results are compared with the approximation of the reference.