Removal of a reactive textile dye (Reactive Blue 221) from aqueous solutions was investigated using a one-step process consisting of simultaneous synthesis of organosepiolite and adsorption of dye. The one-step process was using sepiolite as adsorbent which is in contact with the Reactive Blue 221 dye and the cationic surfactant (cetyltrimethylammonium bromide) in the solution simultaneously. The effects of pH, contact time, temperature, adsorbent amount and surfactant amount on the removal of dye were studied. The kinetic data showed that the adsorption process reached equilibrium in 45 min. The rate of adsorption conformed to the pseudo-second-order kinetics. The experimental adsorption equilibrium data were analyzed with Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models and the most suitable adsorption model was found to be Langmuir isotherm. The Langmuir monolayer capacity was calculated as 159.40 mg/g at 25 degrees C. Various thermodynamic parameters such as Delta G degrees, Delta H degrees and Delta S degrees were estimated and the results show the spontaneity of the adsorption. The adsorbent dose of 4 g/L was found to be sufficient for the removal of dye. The adsorption capacity increased to 350 mg/g when the CTAB was added with the amount of three times the cation exchange capacity of sepiolite. In addition, the amount of adsorption in the one-step process was compared with that obtained in the conventional method using the modified sepiolite as the adsorbent. In addition, the XRD, FTIR and SEM-EDS methods were used to characterize the sepiolite, modified sepiolite and dye-loaded samples. The results showed that the one-step process is an effective, easy and cheaper novel technology for the removal of reactive textile dyes from water.