The nanocrystalline La0.6Pb0.4MnO3 thin films have been grown on (100) SrTiO3 substrates using pulsed-laser ablation technique. The atomic force microscopy and X-ray diffraction measurements show that the films consist of single-crystalline grains of an average size of similar to 17 nm with c-axis perpendicular to the substrate plane. These nanocrystalline films exhibit an enhanced magnetoresistance of > 100% at 1 T in the vicinity of the Curie temperature. Magnetization data suggest that grain boundaries act as tunnel barriers leading to an enhancement in the magnetoresistance. (C) 2002 Elsevier Science B.V. All rights reserved.