The OPERA experiment is designed to study the nm ! nt oscillation observing the nt appearance in a pure nm beam over a base line of 732 km from CERN to Gran Sasso Laboratory. The apparatus consists of a lead/emulsion-film target complemented by electronic detectors and muon spectrometers for muon charge and momentum measurements. The tracking inside the magnets is provide by Bakelite RPC chambers in a large scale application. The commissioning of the RPC system ended in August 2006. The paper present the layout of the RPC system and its performances. & 2009 Elsevier B.V. All rights reserved.