Nanocrystalline Eu3+-doped pyrochlore oxide M2Sn2O7 (M = Gd and Y) has been successfully prepared by a simple and facile hydrothermal synthesis method without the presence of catalysts. The effects of hydrothermal temperature, time and base concentration on the pure phase of the products are investigated. It is found that tuning the base concentration was a crucial step for the control of the pure phase of the M2Sn2O7 (M = Gd and Y) nanocrystals. All the products were systematically characterized by powder X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier-Transform Infrared Spectroscopy (FT-IR), photoluminescence (PL) and photoluminescent excitation spectra (PLE). Furthermore, the luminescence mechanism and size dependence of their spectral properties are also discussed in detail. (C) 2010 Elsevier B.V. All rights reserved.