Abstract: Indirubin isolated from Indigofera tictoria L. (青黛) is an active constituent against chronic granulocytic leukemia, Sixteen N₁'-substituted derivatives of indirubin were synthesized in an attempt to reduce the toxicity and raise the antitumor activity.The phase transfer catalyzed reaction was adopted for preparation of N₁'-substituted derivatives (Ⅱ～ⅩⅢ, ⅩⅤ～ⅩⅦ), except compound ⅩⅣ which was obtained by condensation of N-formylisatin with potassium indoxylate.Compound Ⅲ, Ⅳ, Ⅶ, ⅩⅤ showed higher inhibitory action against Carcinoma W₂₅₆ in rats than indirubin on equal molar basis. Compound Ⅲ is the most potent compound with inhibitory activity of 58%, compared with 30.8% of indirubin in the same experiment.