RSE corrosion monitoring system, partially developed in the frame of UE-DEBCO Project “Demonstration of large scale Biomass CO-firing and supply chain integration”, is presented. The most innovative feature of the system is a probe able to on-line measure the material consumption of the corroded samples exposed into the boiler. The geometry of the sample is similar to that of a section of a tube of SH/RH bundles of the boiler, where relevant corrosion attacks are normally present. Results of four long-term corrosion monitoring campaigns performed in 2009-2011 at ENEL “A.Palladio” power plant of Fusina (VE), which is operated in co-firing of coal and RDF at 5% of the boiler thermal load, are reported. Monitoring was performed both in the boiler combustion chamber and the convective pass, exposing samples in the current operating conditions of the plant or simulating contemporary operation of co-firing and Ultra Super Critical steam cycle. The campaigns showed that a negligible corrosion is present in the convective pass, regardless the exposed material and operation conditions. On the contrary the corrosion grade found at the boiler membrane walls is generally ranked as “significant” and in particular “serious” close to RDF nozzles.