The stable purple-red complex of xylenol orange and scandium (Ⅲ) can be utilized for colorimetric determination of scandium. It is found that the solution should adjusted to pH 2.2-2.45. Optical density should be measured at 560 mμ where the maximum absorption of the complex occurs. Small amounts of trivalent rare earth metals, iron(Ⅲ), manganese(Ⅱ), and aluminum do not interfere, while sulfate, phosphate, fluoride, oxalate, thiourea, ascorbic acid, and nitrilotriacetic acid interfere seriously. Among reductants studied, thioglycolic acid interfere the least. The interference due to thorium can be eliminated by determining thorium separately and then deduce From the sum of thorium and scandium (100μg of thorium corresponds to 41μg of scandium oxide in the xylenol orange determination).