A series of Sm doped LaNiO3 nanoparticles by solids denoted as Lai(1-x)Sm(x)NiO(3-delta) (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1) were synthesized by the modified citrate sol gel method. The prepared compounds were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), BET specific surface area and scanning and transmission electron microscopy (SEM-TEM) techniques. The results showed that highly homogeneous and crystalline oxides with particle sizes in the range of nanometers were obtained through this synthesis method. The XRD patterns of the prepared La1- xSmxNiO3-delta solids confirmed the perovskite structure for the samples up to x = 0.1. When the degree (x > 0.1) of substitution increase the formation of spinel-type La2NiO4 and mixed NiO, Sm2O3 phases are favored thermodynamically and the rate of perovskite structure formation decreased drastically The effects of the partial substitution of La by Sm, reaction temperatures and feed gas ratio at atmospheric pressure were investigated in process of combined carbon dioxide reforming and partial oxidation of methane (CDRPOM), after reduction of the samples under hydrogen. All samples presented similar activity at 1073 K while at lower temperatures, the La1-xSmxNiO3-delta catalysts with x = 0, 0.1, 0.9 and 1 showed the highest activity. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.