Aim:A novel series of N-nitroso-3-(substituted phenylimino)-indolin-2-one 3a–h was synthesized and tested for carcinogenic effects.Materials and Methods:The synthesized pyrazole derivatives’ chemical structures were proved by means of their infra red (IR), proton nuclear magnetic resonance (1H-NMR), and mass,and confirmed by elemental analyses. The carcinogenic activity was assessed by 3–(4,5dimethyl thiazole–2yl)–2,5–diphenyltetrazoliumbromide (MTT) cell-viability assay.Results:The results show that most of the synthesized compounds exhibit significant carcinogenic activities. Among the synthesized compounds, N-nitroso-3-(2,4-dinitrophenylimino)-indolin-2-one 3h exhibited the most potent carcinogenic activity.Conclusion:The structure–activity relationship (SAR) studies show that the nature as well as the position of the amine are important for deciding the activity profile of the indolin-2-one derivatives, which reiterates the need for further experimental investigations.