conventional centrifugal separator wherein an improved rotor according to the preferred embodiment of the present invention referring to this drawing figure there are shown provided a centrifugal separator casing designated at the reference number 1 and a rotor chamber at 2 disposed in the upper part of the casing 1 also seen is a top cover at 3 which is disposed to close the open top of the rotor chamber 2 which top cover 3 is hinged swingably to the separator casing 1 by way of a hinge 4 in the lower central area of the separator casing 1 there is provided a driving motor 5 with its output shaft 6 extending upwardly into the rotor chamber 2 upon the motor output shaft 6 there is mounted operatively a rotor assembly 7 which is to be described in detail later the rotor assembly 7 is as typically shown in fig2 and 3 comprised of a rotor body 8 and a set of buckets each including three types of bucket element 9 10 11 the rotor body 8 is of a cylindrical shape with a closed bottom having as shown in fig4 a and b a plan view and a semi cross sectional view a mount 12 for receiving the output shaft 6 of the driving motor disposed in bottom center thereof and also four bucket receiving sections 13a 13b 13c and 13d defined around the motor output shaft mount 12 in the side wall sections 14a 14b 14c and 14d which define the bucket receiving.