A series of novel naphthalimide derivatives with flexible alkyl/aryl moieties were designed and synthesized. Their antitumor activities were evaluated against HeLa, A549, P388, HL-60, MCF-7, HCT-8 and A375 cancer cell lines in vitro. The preliminary results showed that most of the derivatives had comparable antitumor activities over Amonafide with the IC(50) values of 10(-6) to 10(-5)M. More importantly, flow cytometric analysis indicated that the derivatives could effectively induce G(2)/M arrest and progress to apoptosis in HL-60 cell line after double staining with annexin V-FITC and propidium iodide. The present work provided a novel class of naphthalimide-based derivatives with potent apoptosis-inducing and antitumor activities for further optimization.