The ultra-fine Ni0.49CU0.24Zn0.24Fe2O4 was prepared as a novel material for decomposing CO2 which is the main gas causing "green house effect". The relationships between the microstructure and CO2 decomposition activity of Ni0.49Cu0.24Zn0.24Fe2O4 were investigated. The results showed that H-2-reduced Ni0.49Cu0.24Zn0.24Fe2O4 had higher decomposition performance than MFe2O4 (M = Ni, Cu, Zn) at 310 degrees C. The study of cycle decomposition activity found that Ni0.49Cu0.24Zn0.24Fe2O4 can be used repeatedly at 310 degrees C. Moreover, the analysis of phases and morphology of products by XRD Rietveld analysis, TEM, and Raman, respectively, demonstrated that Ni0.49Cu0.24Zn0.24Fe2O4 was destroyed to carbide, ZnO, and metal alloy and the activity phase changed from spinel structure to metal alloys during the decomposition of CO2. The deposited carbon was in the form of amorphous. (C) 2008 Elsevier B.V. All rights reserved.