An MgB2 superconducting solenoid magnet has been developed for electron beam focusing in X-band (12 GHz) klystrons for particle accelerator RF systems, to provide a central field of 0.8 T at 57 A and at ≥20 K. It has successfully realized significant AC-plug power saving in one order of magnitude compared with that for a conventional Cu solenoid magnet. The large-scale application may be expected for the Compact Linear Collider (CLIC) project proposed as a future accelerator candidate at CERN. It requires ~5,000 klystrons, and the MgB2 magnet application will realize significant AC-plug power saving. This paper describes progress in a prototype MgB2 superconducting solenoid magnet development and discusses the future prospect.