Abstract: The process features of the full-floating, half-floating and restrained mandrel mills as well as the developments of restrained mandrel mills worldwide are briefed. The article respectively describes the outlines, production process flows, major equipment characteristics and performances with respect to φ355.6mm PPM-MPM train in Dalmine, Italy, φ273mm MPM train in Tamsa Co., Mexico, φ244.5mm PPM-MPM train in Fairfield Works, American Steel Co., φ177.8mm MPM train in Algoma Steel Corp. Ltd, Canada and φ250mm restrained mandrel mills both in Siderca Works, Argentina and in General Tianjin Seamless Steel Tube Plant, China.