A cloud point extraction process using mixed micelles of the cationic surfactant CTAB and non-ionic surfactant Triton X-100 to extract thorium(IV) from aqueous solutions was investigated. The method is based on the color reaction of thorium with 5-(2′,4′-dimethylphenylazo)-6-hydroxypyrimidine-2,4-dione (DMPAHPD) in the presence of potassium iodide in hexamethylenetetramine buffer media and mixed micelle-mediated extraction of the complex. The optimal extraction and reaction conditions (e.g. surfactant concentration, reagent concentration, effect of time) were studied and the analytical characteristics of the method (e.g. limit of detection, linear range, molar absorptivity, Sandell sensitivity, preconcentration, and improvement factors) were obtained. Linearity was obeyed in the range of 0.5–15 ng mL⁻¹ of thorium(IV) ion and the detection limit of the method is 0.16 ng mL⁻¹. The interference effect of some anions and cations was also tested. The proposed method was successfully applied for the preconcentration of trace thorium in natural water samples as well as in plant material and soil samples prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES) with satisfactory results.