The last rotor blades of a condensing turbine are subject to increased erosion due to the wet steam flow. Today, no reliable methods are known to determine the erosion process and the life duration of erodes rotor blades so that they can be exchanged or restored in good time. This article contains the results of long-standing observations and investigations on the rotor blades of 664-MW condensing saturated steam turbine -regarding the erosion process and course - in the Nuclear Power Station Krsko. Based on the erosion mechanism at the last rotor blade ring, a samplified formula has been developed for the calculation of the life duration of rotor blades.