We synthesized 13 ABO3 (A = La, Pr, Nd, Sm; B = Cr, Mn, Fe, Co) perovskites by the solution combustion method. The perovskites were characterized by inductively coupled plasma optical emission spectroscopy (ICP OES) or equivalent X-ray fluorescence analysis (XRF), oxygen analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and N2 adsorption. Then, we tested the perovskites in CO oxidation. The preparation procedure, characterization techniques and catalytic testing are described in detail in the Electronic Supporting Information (ESI). XRD reveals that all samples present a perovskite-like structure (Table ). The materials are phase-pure, with the exception of NdFeO3, for which we identified small amounts of a by-phase (2% Nd2O3). The orthorhombic crystal structure is observed for the majority of the synthesized materials. Only LaMnO3 and LaCoO3 perovskites exhibit the rhombohedral crystal symmetry. In order to quantify the distortions of the perovskites with respect to the ideal cubic structure, we determined the observed tolerance factor ! "#$ based on the Rietveld refinement analysis using the expression