A valve rotating mechanism for exhaust valves, especially of marine diesel engines, which mechanism is braced in a valve housing for the valve stem (1) between an upper and a lower drive element, is linked to the lower drive element via a freewheel device, which transmits rotation of the valve stem (1) during closing movement thereof, and is also braced relative to the upper drive element via a rotary cylinder (15), which brings about rotation of the valve stem (1) through engagement with a fixed support cylinder (13). Therein the rotary cylinder (15) and support cylinder (13) are engaged with one another via a helical gearing, wherein the rotary cylinder (15) is linked to the valve stem (1) via the freewheel device and the support cylinder (13) is fastened on the housing side.