The effects of surface modification of Na-montmorillonite (Na-MMT) on morphology and the theological properties of polyethylene glycol/organoclay nanocomposites are investigated. Dodecyltrimethyiammonium bromide (DTABr) is used to modify the clay surface. Adsorption of DTABr on Na-MMT is monitored by zeta potential measurements. From zeta potential measurements, three DTABr concentrations, 1 x 10(-3), 7.5 x 10(-3), and 5 x 10(-2) mol/L, are chosen to fabricate the polyethylene glycol/organoclay composites. The morphology of three sets of organoclays (OMMT1, OMMT2, and OMMT3) is studied by X-ray diffraction (XRD) technique. The increase of basal spacing is found to be 0.2 nm as the DTABr concentration is increased to 7.5 x 10-3 mol/L. The rheological properties of polyethylene glycol (PEG)/organoclay nanocomposites are studied for three organoclays at different PEG concentrations. All nanocomposites show Bingham plastic flow behavior. The OMMT3 shows maximum viscoelastic properties in the polymer matrix. The morphology and electrokinetic properties of the PEG/organoclay nanocomposites are also investigated.