Steel plate shear wall (SPSW), which commonly consists of an unstiffened slender wall panel inside a steel boundary frame, is known as an effective lateral force resisting system in high seismic zones. However, in accelerated construction of high-rise buildings, gravity loads will inevitably be transferred to the wall panel and causing elastic buckling, since it is impractical to fasten all the wall panels to the boundary frame in the last step. In order to avoid buckling of slender wall panels under gravity or in serviceability limit states, channel stiffeners are attached to the wall on one side, with both toes welded to the wall surface to form a closed section and provide higher out-of-plane and torsional constraints. This paper presented experimental research on channel-stiffened steel plate shear walls as a new type of steel plate shear wall system. Cyclic quasi-static tests were conducted on three 1/3-scale two story single-bay specimens, including two specimens with different stiffener arrangement and a similar unstiffened SPSW specimen for comparison. All specimens showed highly ductile behavior and stable cyclic post-buckling performance, and could tolerate at least 4% story drifts. Compared with unstiffened SPSWs, the channel stiffened steel plate shear walls could have higher elastic buckling capacity and lateral strength and significantly higher lateral stiffness. Recommendations on seismic design of stiffened SPSWs were also proposed.