A new series of negatively charged inorganic-organic hybrid membranes were prepared by the sol-gel and oxidation processes of 3-(mercaptopropyl) trimethoxysilane (MPTS). The membranes were conducted IEC, streaming potential, and pure water flux measurements as well as SEM observation, FTIR and TGA analysis. It is shown that IECs of the membranes increase with an increase of the coating times within a range of 1.0 x 10(-2) to 2.3 x 10(-2) meq. cm(-2) for 1-4 coating times. The negative charge of the membranes was tested by FTIR spectrum, IEC measurements as well as streaming potential values. The thermal stability was approved by TGA results which showed that the membranes could endure a temperature as high as 250 degreesC. The average pore diameter evaluated from pure water flux measurements ranged from hundreds of nm to several nm, depending mainly on the coating times and somehow on the sol composition. Thus, by changing the coating times and sol composition, a series of membranes can be obtained to comply with the request for different pressure-driven processes. (C) 2003 Elsevier B.V. All rights reserved.