A sensitive method for carbon tetrachloride (CCl(4)) determination has been developed with the aid of ultrasonic oxidation decolorization of methyl orange (MO). It is found that the ultrasonic oxidation decolorization rate of MO can be significantly promoted by adding a little amount of CCl(4). The increased ultrasonic decolorization rate of MO is strongly dependent on the concentration of CCl(4) added, and a linear correlation is observed between the amount of CCl(4) and the decolorization rate of MO in the ultrasonic oxidation process. Thus, the CCl(4) determination is transformed to a simple and direct determination of the decoloration extent of MO solution at a given concentration. As an indirect spectrophotometric determination of CCl(4), the new method is sensitive and easy of operation with a maximum wavelength of 508 nm, molar absorptivity of 3.83 x 10(4) L mol(-1) cm(-1), and a Sandell sensitivity of 7.96 x 10(-3) microg cm(-2). Under optimized conditions, Beer's law is obeyed in the range of 0.4-20 mg L(-1) of CCl(4) (DL=0.19 mg L(-1), r=0.9996). The concentrations of CCl(4) in several practical samples have been determined satisfactorily by using this method.