A magnetic-drive centrifugal pump comprises a driving motor, a pump shaft, an impeller, a rotor with a sleeve portion to which is connected the impeller, the rotor and impeller being rotatably mounted on the pump shaft, and a pump casing consisting of a front casing and a rear casing. The impeller is driven by a magnetic coupling formed by a driving magnet provided on a magnet holder connected to the driving motor and an impeller magnet provided in the rotor. The sleeve portion has an outer diameter smaller than an outer diameter of a main portion of the rotor. The rear casing has at a location opposite to the sleeve portion a first inner diameter enabling an outer circumference of the main portion of the rotor to slide therein, and at a location opposite to the main portion of the rotor a second inner diameter larger than the first inner diameter. One end of the pump shaft is journaled in a boss in an inlet of the front casing and the other end of the pump shaft is journaled in a rear wall of the rear casing. With this arrangement, the pump according to the invention is very easy to assemble and disassemble to facilitate its maintenance and inspection of parts.