Many marine alkaloids possess interesting structures and antitumor activities. Thus, we have synthesized (2E,4E)-4-arylidene-2-styryl-5-oxopyrrolidine derivatives of the marine alkaloids, rhopaladins A-D. The cytotoxicities of these derivatives against C-33A, CaSki, SiHa, HeLa, HepG2, and LO2 cells are evaluated by MTT assays. The results show that (2E,4E)-2-(4-chlorostyryl)-4-benzylidene-N-cyclohexyl-1-(4-fluorophenyl)-5-oxopyrrolidine-2-carboxamide significantly inhibits cancer cell proliferation, with IC50 values against C-33A, CaSki, SiHa, HeLa, and HepG2 cells of 5.56, 9.15, 12.5, 21.4, and 14.5 mu M, respectively, and an IC50 value of 86.77 mu M against the normal LO2 cell line.