Single-phase RMn2O5 (R = Gd and Sm) nano- and microstructures have been successfully synthesized via a simple hydrothermal process at 250 degrees C for 24 h using NaOH as mineralizer. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selective area electron diffraction patterns (SAED) were used to characterize the as-synthesized GdMn2O5 and SmMn2O5 samples. The effect of NaOH concentration and the molar ratio of Mn2+/Mn7+ on the morphology and size of the final products was studied, and a possible formation mechanism of RMn2O5 (R = Gd and Sm) nanoplates and nanorods under hydrothermal conditions was proposed. (C) 2009 Elsevier B.V. All rights reserved.