The invention refers to a drive unit (1) for a centrifuge rotor (2) of a centrifugal separator. The drive unit (1) includes a drive shaft (3), which is arranged to support said centrifuge rotor (2) and is rotatably journalled around an axis (z) of rotation, a casing (6), which forms an inner space for the drive shaft (3), and a drive motor shaft (9), which is provided outside the casing (6) and connected to the drive shaft (3) by means of a transferring member (11) which extends through a passage (12) in the casing (6). A shielding member (23) is provided inside the casing (6) in such a way that the part of the transferring member (11), which is located inside the casing (6) is shielded from the inner space, wherein the shielding member (23) forms a channel, which extends through the casing (6) and is shielded from the inner space of the casing.