In an attempt to develop potent and selective antitumor agents, a series of novel 3-amino-4-indolylmaleimides were designed and synthesized. The reaction showed high regioselectivity. The structure of compound 7a was determined by an X-ray single crystal diffraction method. The cytotoxicities of the title compounds were evaluated against HeLa, SMMC 7721 and HL 60 cancer cell lines by a standard MTT assay in vitro. The pharmacological results showed that some of the title compounds displayed moderate or high cytotoxic activity against the tested cell lines. Compound 7d was the most promising compound against the tested cancer cell lines. Structure-activity relationships are discussed based on the experimental data obtained. A hydroxyethylamino group at the 3-position in the side chain of indolylmaleimide is associated with an increase in cytotoxicity.