Abstract: This paper presents experiments and finite element analyses of seismic behavior of 14 single layer and single span frames of cold-formed double C steel with gusset plates. The effects of gusset plate thickness, frame span, C steel thickness, C steel flange width-thickness ratio, and C steel web depth-thickness ratio on the seismic behavior of the frames were discussed. Hysteretic curves and skeleton curves were presented, and the failure mode and seismic behavior were analyzed. It is noted that the frame showed in-plane instability with local buckling of the beam ends and column bases. Ensuring strong nodes, the plate thickness had less influence on the bearing capacity and seismic behavior. Increasing section parameters of the C steel, the bearing capacity of the frame increased accordingly. As the C steel thickness increased, the ductility of the frame increased. This frame showed stable bearing capacity degradation, and good ductility, energy dissipation capacity, and seismic behavior. It is proposed that the stiffness ratio of column to beam is no less than 0.4.