Gold complexes (GC) reveal antitumor activity against xenografts of human tumors as well as against transplantable animal tumors in vivo and demonstrate cytotoxic effect against the wide spectrum of human tumor cells in vitro. GC had been effective against tumors with the acquired resistance to the platinum compounds. It is revealed the strong difference between mechanism of action of GC and platinum derivatives. Proteins, mainly thioredoxin reductase and proteasoma 26S, are the principal targets for the GC action but not for the platinum derivatives impact. Thioredoxin reductase and proteasoma 26S activity inhibition by GC leads to the development of the apoptosis mainly by the mitochondrial way in tumor cells.