A chromium-benzenedicarboxylate (Cr-BDC) named MIL-101 with huge porosity, one of the most widely studied metal-organic framework (MOF) materials, has been synthesized in wide range of reaction conditions like various water concentrations. pHs and synthesis methods (electric heating and microwave irradiation) to get nano-sized crystals. The crystal size decreases with increasing water concentration and pH. The decrease of size in diluted reactants may be explained with a smaller rate of crystal growth than nucleation rate. The decreased size of MIL-101 in diluted condition is different to the synthesis of zeolites, probably because MOFs are obtained by a simple process of complexation. Moreover, high pH may be beneficial to produce not only benzenedicarboxylate but also chromium trimers, which are needed for the nucleation of MIL-101 structure. In a selected condition, the MIL-101 having the size of about 50 nm can be obtained facilely and reproducibly with relatively high yield, which may lead to enlarging the applications of the valuable MOF material. (C) 2010 Elsevier B.V. All rights reserved.