Mesoporous microspheres of light rare earth (La, Ce, Pr, Nd) hydroxycarbonates and oxides were successfully fabricated by a facile surfactant free hydrothermal method in supersaturated aqueous urea solution. The techniques of XRD, TEM, SEM, TG/DTA and N(2) adsorption-desorption were employed to investigate the structure and formation process of mesoporous microspheres. It was revealed that supersaturated urea not only serve as a reactant and pH modifier in the reaction system but also guide the oriented assembly of hydroxycarbonate crystallites into microspheres by acting as a structure-directing agent. The microspheres of rare earth oxides could easily be obtained by simple calcination of corresponding hydroxycarbonates precursors without undergoing morphology changes. In addition, the influences of rare earth precursor and urea concentrations on the formation of microspheres were also investigated. (C) 2011 Elsevier Ltd. All rights reserved.