The compounds [(η6‐p‐cymene)RuCl2(4‐nitroaniline)] and [(η6‐p‐cymene)RuCl2(2‐halogen‐4‐nitroaniline)] were synthesized and characterized by various means. The [(η6‐p‐cymene)RuCl2(4‐nitroaniline)] and [(η6‐p‐cymene)RuCl2(2‐fluoro‐4‐nitroaniline)] compounds were determined by X‐ray diffraction, appearing in a distorted piano‐stool type of arrangement with similar bond lengths and angles around the ruthenium. The compounds exhibited moderate to strong in vitro cytotoxicity against A549 and MCF‐7 human cancer cells. Substitution of heavy halogen atom on the ortho position of para‐nitroaniline weakened the cytotoxicity against both of MCF‐7 and A549, except the cases of fluorine substitution for hydrogen atom regarding A549 and bromine substitution for chlorine atom regarding MCF‐7, which showed minor deviation.