This study deals with the synthesis of novel 2- (2,3-dioxo-2,3-dihydro-1H-indol-1-yl)-N-phenylacetamide derivatives (6a–j) from isatin (3) and 5,7-dibromoisatin (4). All newly synthesized compounds were characterized using IR, 1 H NMR, MS, and elemental analysis followed by evaluation of their cytotoxic activity by XTT assay on breast cancer cell line MCF-7 and non-cancer African green monkey cell line VERO. Correlation study for QSAR and in vitro assay was performed. The outcomes indicated that electron withdrawing substitutions at para position of phenyl ring and 5, 7 positions of isatin ring and increasing lipophilicity of the compound increased the cytotoxic activity. The 2-(5,7-dibromo-2,3-dioxo-2,3-dihydro-1H-indol-1-yl)- N-(4-nitrophenyl)acetamide (6b) was found to be the most active compound in the series and demonstrated higher selectivity toward MCF-7 cell line. The IC50 values were 1.96 and 1.90 lM for test compound (6b) and vinblastin (reference drug), respectively. This indicates compound (6b) may possess equipotent cytotoxic activity to vinblastine. The compound (6b) is particularly promising, since it could kill cancer cells 19–20 times more effectively than the non-cancer cells. This property of (6b) may enable us to effectively control tumors with low side effects. Hence, we propose that 2-(5,7-dibromo-2,3-dioxo-2,3-dihydro-1Hindol-1-yl)-N-(4-nitrophenyl)acetamide may be used as lead for further development.