Abstract: A method for the colorimetric determination of protocatechualdehyde has been deve-loped in the presence of protocatechuic acid. The optimum conditions are as follows: to the protocatechualdehyde sample is added 5.0 ml of 1:1 cold mixed solution of 2% phlo-roglucinol solution (in ethanol)and concentrated sulfuric acid. After having been sha-ken, the mixture and the reagent blank are warmed in a water bath at 50℃ for 5 minutes and then cooled immediately with cold water. The colorimetric measurement is made at 496 nm against a reagent blank. The standard curve is linear in the range of 1～12μg of protocatechualdehyde. This method is fairly sensitive, simple and reproduc-ible, it can be used in pharmacological studies and for the determination of protocate-chualdehyde in crude drugs and pharmaceutical preparations.