The present invention relates to hydroxylated indirubin derivatives having the formula (I) wherein the group R represents a straight-chain or branched-chain alkyl group or a straight chain or branched-chain alkoxy group each having 1 to 18 carbon atoms, the group R′ represents H, a straight-chain or branched-chain alkyl group having 1 to 4 carbon atoms or a glucuronide group, and X is H or OH; which can be used for the manufacture of a medicament for the treatment of solid cancers and leukemia and metastases thereof.