The indigotin and indirubin contents of Radix Isatidis, its aqueous extract and residues, as well as extract with 95%, 50% alcohol were determined by TLC-densitometry. The authors throw doubt upon the current processes of extracting with water and precipitating with alcohol for Radix Isatidis, and indicate that the method of extraction with alcohol can give more indigotin and indirubin.