Ultracentrifuges that are operable at 100,000 x g or higher RCF are used for separation of nano-order microparticles. For pelleting particles, conical tubes are helpful. Among conventional Hitachi Koki rotors, the S55A2 angle rotor is operable at 201,000 x g with the 1.5-ml micro tubes (conical bottom). This time, the new P50A3 angle rotor is developed for use with ultracentrifuges. This rotor is operable at 250,000 x g with twenty-four 1.5-ml micro tubes at a time. For more efficient pelleting, the tube cavity angle of the P50A3 angle rotor is similar to that of a swing rotor in addition to the conically shaped bottom. The P50A3 angle rotor is suitable for separation of many virus samples.