La0.67Sr0.33MnO3 thin films have been prepared by pulsed laser deposition on (100) SrTiO3, (100) Si and YSZ/CeO2 buffered (10 0) Si substrates. Structural, electrical and magnetic characterisations were performed on each film, in order to put in evidence the grain boundaries effect in the magnetotransport properties. The films show a significant colossal magnetoresistance (CMR) effect near the Curie temperature. Textured and polycrystalline films show an additional magnetoresistance effect at low temperature originating on spin-polarised carriers tunnelling through grain boundaries or a non-ferromagnetic surface layer. The MR behaviour as a function of magnetic field and temperature shows that the suppression of magnetic fluctuations is the origin of the magnetoresistance in epitaxial films, while the intergrain effects dominate the MR in textured and polyerystalline films. (C) 2002 Elsevier Science B.V. All rights reserved.