Bladders are important rubber parts used for shaping and curing of tires. These parts are exposed to high temperature, high pressure, medium-large extension, and oxidative,e aging during their service life. Curing bladders are usually made of butyl-based rubber Compounds vulcanized with phenolic resin Vulcanization systems. To study the effect of Montmorillonite nano-clay on properties of these rubber parts and their functionality during service, the most compatible and well dispersed organically modified Montmorillonite (OMMT) nano-clay has to be selected. To study the effects of organic modifier on properties of these compounds, five types of commercial OMMT were mixed with the compounds using the melt intercalation method. Effect of modifiers on compatibility between clay and rubber, dispersion of clay in the polymer matrix, and thus mechanical properties of the nano-composite were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), mechanical tension, and dynamic-mechnical-thermal analysis (DMTA). XRD results revealed an intercalated structure for all OMMTs, but with different degrees of rubber intercalation. The largest change in interlayer spacing of silicate layers due to intercalation of rubber was seen for an OMMT modified by dimethyl-benzyl-hydrogenated tallow, quaternary ammonium. AFM and SEM micrographs of the latter compound confirmed the intercalated structure with a good distribution of filler. Viscoelastic Properties obtained from DMTA confirmed more compatibility between butyl-based rubber compoung and this OMMT. This modified clav was selected as the filler of choice for potential application in actual bladder compound. Uni-axial tension tests Could also differentiate among nano-composites reinforced with differently modified clays. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2101-2109, 2010