New beta-aryl-alpha-dimethoxyphosphoryl-gamma-lactams 4a, b were designed and synthesized through the intra-molecular cyclization of 3a, b obtained from the addition reaction of methyl 2-(dimethoxyphosphoryl)acetate to (E)-2-(2-nitrovinyl)thiophene and (E)-2-(2-nitrovinyl)furan, respectively. The in vitro cytotoxicity of these compounds was evaluated against human breast cancer (MCF-7), rat glioblastoma (C6), prostate cancer (PC3), neuroblastoma (SHSY-5Y), and mouse fibroblast cell lines (L929). Dimethyl (4-(furan-2-yl)-2-oxopyrrolidin-3-yl)phosphonate (4b) was found to have cytotoxic activity towards MCF-7 and PC3 cell lines at the concentration values above 5 mM and 6 mM, respectively (IC50 values of MCF-7, 5.92 +/- 1.86; PC3, 6.70 +/- 2.10 mM). Dimethyl (2-oxo-4-(thiophen-2-yl)pyrrolidin-3-yl)phosphonate (4a) only decreased the viability of MCF-7 cells at 8 mM concentration (IC50 value of MCF-7 5.67 +/- 1.70 in mM). In addition 4a, b had shown no significant cytotoxic effect on C6, SHSY-5Y and L929 cell lines.