A series of novel pyridazinone derivatives bearing benzenesulfonamide moiety (2a-h) has been synthesized by the condensation of appropriate aroylacrylic acid and 4-hydrazinobenzenesulfonamide hydrochloride in ethanol. Five derivatives (2a, 2b, 2d, 2g and 2h) were evaluated for their anticancer activity toward human cancer cell lines by the National Cancer Institute. The 2h showed remarkable activity against SR (leukemia) and NCI-H522 (non-small cell lung) with a GI(50) value of less than 0.1 μM. It also displayed good activity against leukemia (CCRF-CEM, HL-60 (TB), K-562, MOLT-4, RPMI-8226), non-small cell lung cancer (NCI-H460), colon (HCT-116, HCT-15, HT29, KMI2, SW-620), CNS (SF-295), melanoma (MALME-3M, M14, MDA-MB-435 SK-MEL-5), ovarian (OVCAR-3, NCI/ADR-RES) and breast (MCF7) cancer cell lines with a GI(50) less than 1.0 μM. The acute toxicity study of 2h indicated that it is well tolerated intra-peritoneally (400 mg/kg) by athymic nude mice. The 2h may possibly be used as lead compound for developing new anticancer agents.