A castor includes an upright support post, a brake ring secured on the support post, a castor body rotatably mounted on the support post, two rollers rotatably mounted on the castor body, a first locking member movably mounted on the castor body, a second locking member movably mounted on the castor body, and a brake handle pivotally mounted on the castor body. Thus, when the castor is locked, each of the two rollers is locked onto and cannot be rotated relative to the castor body, and the castor body is locked onto and cannot be rotated relative to the support post, so that the castor will stop rotating when being braked so as to provide a double-braking effect.