In this study, a series of nanocomposite membranes consisted of organic polyimide and organo-modified clay were successfully prepared by an in situ polymerization through thermal imidization reactions using a dual-(i.e., CTAB/melamine) and mono-organic modifier as swelling agent of clay mineral. A sequential comparative study was performed to investigate the effect of various feeding ratios of dual- and mono-organic modifiers on the physical properties of as-prepared samples. The as-synthesized nanocomposite membranes were subsequently characterized by WAXRD and TEM. It should be noted that all the nanocomposite membranes prepared from a dual-organic modifier system exhibited a better dispersion of silicate layers in PI matrices as compared with that of mono-organic modifier system. Comparative studies for the effect of various feeding ratios of dual- and mono-organic modifiers on the thermal stability, mechanical strength, molecular barrier properties, and optical clarity of PI-clay nanocomposite membranes were performed with measurements of TGA, DSC, DMA, GPA, VPA, and UV-visible transmission spectroscopy, respectively. (C) 2008 Wiley Periodicals, Inc.