A simple and effective method has been developed for the preconcentration of trace amount of thorium by cloud point extraction (CPE) using arsenazo-Ill as complexing agent prior to its UV-Visible spectrophotometric determination. A placket-burman design (PBD) was used to determine the main factors such as pH (P), amount of triton X-114 (TX-114), cetyltrimethylammonium bromide (CTAB), ligand volume (LV), addition salt (Sty) and temperature (T). Under optimum conditions, the influence of significant variables including pH, TX-114, and LV on the quantitative extraction efficiency of Th (IV) were investigated by Central 2(3) + star composite design (CCD). Interference effect of some anions, cations and some metals was also studied. The limit of detection was found to be 0.46 mu g/L with preconcentration factor of 50. The relative standard deviation of the method was <5%. The method was successfully employed for the determination and preconcentration of thorium in rock sample.