A novel series of indolin-2-one derivatives containing the 4-thiazolidinone moiety (5a-5p) was synthesized and the cytotoxicity of these derivatives was evaluated in vitro against three human cancer cell lines (HT-29, H460 and MDA-MB-231) by standard MTT assay. Some prepared compounds exhibited significant cytotoxicity against different human cancer cell lines. Several potent compounds were further evaluated against one normal cell line (WI-38). In particular, the promising compound 5h showed remarkable cytotoxicity and selectivity against the HT-29 and H460 cancer cell lines (IC(50) = 0.016 µmol/L, 0.0037 µmol/L, respectively).