Isatin, 1H -indoline-2,3-dione, an endogenous compound, is also a synthetically versatile molecule that possesses a diversity of biological activities including anticonvulsant, antibacterial, antifungal, antiviral, anticancer, and cytotoxic properties. Based on the promising cytotoxic activity studies on N -substituted isatin derivatives, a series of 18 derivatives of 2-(2,3-dioxo-2,3-dihydro-1H -indol-1-yl)-N-phenylacetamide were designed, synthesized, and characterized according to their analytical and spectral data. All of the compounds were evaluated for their cytotoxic activity against MCF7, A549, HeLa, and HEK293 cell lines by real time cell analyzer. Etoposide was used as a standard compound. Briefly, ortho substitutions gave better results compared to meta and para substitutions on the N−phenyl ring and compounds bearing ortho substitutions were more effective on MCF7 cell lines than A549 and HeLa cell lines. 2-(2,3- Dioxo-2,3-dihydro-1H -indol-1-yl)-N-(2-isopropylphenyl)acetamide was the most active compound against all the tested cell lines.