Organoclays containing various amounts of stearic acid (SA) were synthesized, and clay/polystyrene-block-polybutadiene-block-polystyrene triblock copolymer (SBS) intercalated nanocomposites were prepared using organoclays containing SA by melt-blending. Montmorillonite was the clay used, and both stearylamine and SA were used as surface modifiers. The amount of SA added was 0, 20, 50 and 100% of the cation-exchange capacity (CEC). In this study, the effects of SA on the microstructure and mechanical properties of the clay/SBS nanocomposites were investigated. In clay/SBS with 100% CEC of SA, although no exfoliation of the clay occurred, the stacked clay layers were uniformly dispersed at the nanometer level (100-800 nm) without agglomeration. Clay/SBSs containing SA exhibited superior mechanical properties compared to clay/SBS without SA. It was found that SA effectively improved the clay dispersion in the SBS matrix and the mechanical properties of the clay/SBSs. (c) 2006 Society of Chemical Industry.