Abstract: The present invention provides an automatic balancing rotor for centrifuges which is capable of compensating for imbalance of a centrifugal force occurring due to a weight difference of samples. The automatic balancing rotor includes a plurality of rotating arms (29) which is spaced out at regular angular intervals, with a plurality of buckets (31) containing the samples therein supported by the rotating arms (29). The automatic balancing rotor further includes a balance weight (15) which is provided in each of the rotating arms (29) to be movable in a radial direction, thus compensating for imbalanced centrifugal force applied to the buckets (15), and a balance weight moving means which horizontally moves the balance weight (15) in the radial direction of each of the rotating arms (29).