Magnetorheological fluid is composed of micro-size carbonyl iron (CI) particles for polishing of optical substrates. In this paper, the corrosion resistance of carbonyl iron (CI) particles modified with three inorganic thin films based on rare earth elements, including cerium oxide (CeO2), lanthanum oxide (La2O3) and praseodymium oxide (Pr2O3), was investigated. The morphology and chemistry of the CI-Ce, CI-Pr and CI-La particles were examined by high resolution Field Emission-Scanning Electron Microscopy (FE-SEM), X-ray energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests were carried out to investigate the corrosion behavior of CI particles in aquatic environment. In addition, the Vibrating Sample Magnetometer (VSM) technique was utilized for determination of magnetic saturation properties of the coated particles. Afterwards, gas pycnometry and contact angle measurement methods were implemented to evaluate the density and hydrophilic properties of these particles. The results showed that deposition of all thin films increased the hydrophilic nature of these particles. In addition, it was observed that the amount of magnetic saturation properties attenuation for Pr2O3 and La2O3 films is greater than the CeO2 film. The EIS and polarization tests results confirmed that the CI-Ce had the maximum corrosion resistant among other samples. In addition, the thermogravimetric analysis (TGA) showed that the ceria coating provided particles with enhanced surface oxidation resistance. (C) 2017 Elsevier B.V. All rights reserved.