The hydrolysis of [Ru(η6-p-cymene)Cl2(PTA)] (PTA = 1,3,5-triaza-7-phosphatricyclo-[220.127.116.11]decanephosphine; RAPTA-C) was studied using UV-visible (UV-vis) spectrophotometry and NMR spectroscopy. In analogy to in silico studies, [Ru(η6-p-cymene)Cl(H2O)(PTA)]+ was the most abundant hydrolysis product, although the dihydrolyzed species [Ru(η6-p-cymene)(OH)(H2O)(PTA)]+ and the dichloro compd. are present. Rate consts. for the different aquation and anation steps and the equil. consts. were detd. Hydrolysis is suppressed at high chloride concns. These results have important implications on the mode of action of the RAPTA drug candidates.