Abstract: The acid hydrolysis of [Pt(NH3)3Cl] has been shown to occur to a measurable extent. for this reaction: [APt(NH3)cCl]+ + H2O [chemical equilibrium symbol with rate constant k-1 above and k1 below] [Pt(NH3)c(H2O)]++ + Cl-, the equilibrium quotient was measured at 25 degree C and 35 degree C. At 25 degree C this quotient was 8.4 x 10-5 at [Mu] (ionic strength) = 0 and 25 x 10-5 at [mu] = .318 M. This variation is consistent with the expected changes in activity coefficients. [Delta]H for the reaction was found to be approximately 0. The rate constant, k1 was 2.3 x 10-5 sec.-1 at 25 degree C and it was nearly independent of ionic strength. The acid hydrolysis provides a mechanism for the exchange of the chloride ligand and Cl-. Exchange experiments with Cl36 showed that in addition to the acid hydrolysis, a process, first order in both, [Pt(NH3)3Cl] and Cl- with a rate constant of 6. 10-5 sec.-1M.-1 contributes to the exchange. The behavior of the entire series of chloro-ammines of platinum(II) toward acid hydrolysis and chloride exchange has been summarized, and a likely mechanism for the process has been discussed.