Abstract: In a total volume of 25 mL, 4.0 mL of iso-propanol were added to the color reaction mixture containing a definite amount of Cu(Ⅱ), 0.5 mL of 50 g·L-1 Tween-80 solution, 2.0 mL of pH 9.6 borax-NaOH buffer and 1.0 mL of 0.5 mg·L-1 Cadio-alcoholic solution, and the absorbance of the solution was measured at 498 nm after reacting for 20 min. It was shown that the value of absorbance of the complex formed by Cu(Ⅱ) with cadion was raised to an extent of ca. 30% due to the addition of iso-propanol. Apparent molar absorptivity of the reaction system found was 1.23×105L·mol-1·cm-1. Range of linearity of Cu(Ⅱ) was found to be within 0.28 mg·L-1. Detection limit (3s/k) found was 6.7×10-3mg·L-1. Recovery was tested by standrd addition method using water samples as matrixes, average recovery found was 98.2% with RSD′s (n=7) less than 1.5%.