Reaction of [PtMe(C^N)(SMe2)] (C^N = 2-phenylpyridinate (ppy); 1a, C^N = benzo[h]quinolate, (bhq); 1b) with hydrogen peroxide gives the platinum(IV) complexes trans-[PtMe(OH)2(C^N)(H2O)] (C^N = ppy; 3a, C^N = bhq, 3b) bearing platinum-oxygen bonds. The Pt(II) complexes 1a and 1b have 5dπ(Pt)→π*(C^N) MLCT band in the visible region which is used to easily follow the kinetic of its reaction with H2O2. The kinetics and mechanism of Pt−O bond formation have been experimentally and theoretically investigated, showing the simple second-order kinetics; rate = k2[H2O2][Pt(II) complex]. The Pt(IV) products were characterized by NMR spectroscopy and elemental analysis. The geometries and the nature of the frontier molecular orbitals of Pt(IV) complexes containing Pt-O bonds were also studied by means of the density functional theory. Complex 3b is unstable during the crystallization process in CH2Cl2/acetone and gives the binuclear complex [Pt2Me2(Cl)2(μ-OH)2(bhq)2], 4.