4-Methoxy-2´-chlorodibenzoylmethane forms 1,2 greenish yellow complex with Th(lV) at pH 2.5 to 3.5 with working wavelength 395 nm and gives absorption maxima at 390 nm. Values of molar absorptivity, Sandell's sensitivity, stability constant (log K) and free energy of formation were found to be 15,000 cm^–1 mol^–1, 0.015 μg cm^–2, 9.0526 and –12.428 kcals per mole respectively. Beer's law is valid in the concentration range 1 x 10^–5M to 6 x 10^–5M.