Abstract The adsorption of rhodamine B by montmorillonite and laponite has been studied by visible (absorption and emission) and infrared spectroscopy, and X-ray diffraction. The dye is adsorbed as a uni-charged cation by a mechanism of cation exchange. The amount of this cation and consequently the degree of adsorption depend on pH and on the dye concentration. The adsorbed cationic dye is located in the interlayer space. Due to steric hindrance no π interactions occur between the clay and the aromatic compound and no metachromasy is observed.