Abstract: A rotor for centrifugal separation of liquid specimens introduced on a microplates or a collective unit of microtubes in form of microplates (box type specimen holder) under centrifugal acceleration. Within the rotor, specimen receptacle are placed in radial direction with respect to the axis of rotation, the box type specimen holder is placed in each of the specimen receptacles, and there is provided a member for preventing the box type specimen holder from falling down, or a pad is arranged between the box type specimen holder and inner wall in parallel to the axis of rotation, and centrifugal force to be applied on the box type specimen holder is received by the pad, which is designed in such shape as to approximately follow the shape of the outer wall, and centrifugal separation can be performed with the specimen receptacle inserted from above.