Gold(III) complexes, isostructural and isoelectronic with plati-num(II) complexes, are of potential interest as antitumor drugs. We prepared four representative square planar gold(III) complexes – [AuCl 3 (Hpm)], [AuCl 2 (esal)], [AuCl(dien)]Cl 2 and [Au(en) 2 ]Cl 3 – and characterized them both in the solid state and in solution. Thereafter, the cytotoxicity of these compounds was evaluated in vitro against the A2780 human ovarian tumor cell line that was used as the reference cell line. Remarkably, all these gold(III) com-plexes showed significant cytotoxic effects, [AuCl 2 (esal)] showing a potency comparable to cisplatin. The present gold(III) complexes were also tested on the corresponding cisplatin-resistant line and revealed they were able to overcome resistance to cisplatin to a large extent. The implications of these findings for the develop-ment of new gold(III) complexes to be tested as antitumor agents are discussed.