Full text can be accessed at http://www.sciencedirect.com/science/article/pii/S0304885305000715We report in this work, study on colossal magnetoresistance (CMR) effect in epitaxial La2/3Ca1/3 MnO3 thin films grown on SrTiO3 (0 0 1) substrates by pulsed laser deposition (PLD) technique. The films were grown on as-received SrTiO3 substrates and on SrTiO3 substrates prepared by HF etching (Koster et al., Appl. Phys. Lett. 73 (1998) 2920; V. Leca et al., Wet etching methods for perovskite substrates, University of Twente, MESA+ Research Institute, Low Temperature Division). Two of the samples were annealed in different conditions to investigate the films heat treatment effect on electric and magnetic properties. Electrical resistance was done using the four-probe method at temperatures in the range of 2–375 K without a magnetic field and in an external field of 5 T applied in the film plane. Resistance-magnetic field (R vs. H) at 77 K for the two annealed samples was done in a 5 T sweep magnetic field. The surface morphology and structural information of the films were obtained using atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. Secondary ion mass spectroscopy (SIMS) analysis was performed on the annealed samples to investigate any possible chemical reaction between La2/3Ca1/3MnO3 thin films and SrTiO3 substrate.