Abstract: It was found that by the addition of a definite amount of 4-(pyridylazo)-resorcinol (PAR),the chromogenic reaction of Sc(Ⅲ) with T-(4-TMAP) P was catalyzed and gone to completion in a borate buffer medium of pH 7.6 and when heated in a boiling water bath.The absorption maximum of the complex was found at 421 nm.The apparent molar absorptivity (ε421) was found to be 7.94×106L·mol-1·cm-1,and the linearity range was in the range of 0 to 0.04 μg per 10 mL of solution.The composition ratio Sc∶T-(4-TMAP) P was found as 1 to 2.After completion of color reaction,no significant change in absorbance of the colored complex was observed in 3 h.The stability constant of the complex was determined and a value of 3.1×106(k) was obtained.In the analysis of a titania sample,recovery test for scandium was made by standard addition method,and results obtained were in the range from 92.0% to 97.5%.The mechanism of the catalytic effect of PAR was studied and conclusion was drawn priliminarily as follows: ① an active intermediate complex was formed between Sc(Ⅲ) and PAR,which made a change of the solution condition and made it easier to replace the proton from the porphrin ring;② an ion-association complex was formed between the negatively charged PAR and the positively charged T-(4-TMAP) P,leading to a distortion of the porphrin ring and making it easier to react with the active intermediate complex of scandium.