A new series of thiourea derivatives were obtained by the reaction of 4‐(4‐fluorophenoxy) aniline with different isothiocyanates. Their chemical structures were confirmed by ultraviolet (UV), infrared (IR), nuclear magnetic resonance (NMR), and mass spectral data and elemental analysis. All the synthesized thiourea derivatives were evaluated for their in vitro cancer activity against the human breast cancer cell lines MCF‐7 (human breast adenocarcinoma) and SKBr‐3 (human epithelial breast adenocarcinoma). Most of the derivatives exhibited significant anticancer activity. Especially, compound 3 showed the most potent activity (IC50 20.1 μM) against SKBr‐3 when compared with the drugs 5‐fluorouracil and cisplatin, and, most importantly, it did not affect normal breast epithelial cells (4010).