The partial substitution of Co by Ru in lanthanum cobaltite perovskites (LaCo1-xRuxO3, x=0.05 and 0.2) and its influence on the reducibility and structural modifications in the perovskite lattice have been evaluated by N-2 adsorption isotherms, in situ X-ray diffraction (XRD), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). Characterization of LaCo1-xRuxO3 perovskite precursors reveals that Ru is incorporated into the perovskite lattice, producing a distortion of the original rhombohedral structure, a decrease in mean crystallite size and some increase in the surface area. The structural evolution of the LaCo1-xRuxO3 precursors under a reductive treatment indicates that Ru promotes the reducibility of the perovskite leading to a greater reduction degree of cobalt species. Moreover, the smaller perovskite crystallites obtained with the partial substitution of cobalt by ruthenium evolve to smaller crystal domains of both Co-0 and La2O3 after reduction. The catalysts formed after the reduction of perovskite precursors present very high catalytic efficiency to extract hydrogen from diesel molecules by oxidative reforming. However, those catalysts derived from Ru-substituted perovskites show better catalytic performance associated with the higher development of active metallic phases achieved on the surface of these catalysts. Additionally. Ru promotes the catalytic activity and stability for this reaction increasing the reduction degree of cobalt and decreasing coke formation and sulfur poisoning through the formation of smaller cobalt crystallites. (C) 2011 Elsevier B.V. All rights reserved.