Novel cis- and trans-(silyl)(methyl)platinum(II) complexes were prepared and their reactivity toward reductive elimination was examined. Treatment of trans-PtCl(SiPh(3))(PMePh(2))(2) (1) with an excess amount of MeLi in THF followed by methanolysis of the reaction system gave cis-PtMe(SiPh(3))(PMePh(2))(2) (2), selectively. On the other hand, reaction of 1 with Me(2)Mg in THF formed trans-PtMe(SiPh(3))(PMePh(2))(2) (3). The structure of cis-2 was determined by X-ray diffraction study. Crystal data for cis-2.Et(2)O : monoclinic, space group P2(1)/c, a = 16.113(3) Angstrom, b = 11.354(3) Angstrom, c = 25.216(2) Angstrom, beta = 104.73(1)degrees, V = 4461(1) Angstrom(3), Z = 4, d(calcd) = 1.405 g cm(-3), R = 0.038, R(w) = 0.033, S = 1.72. Thermolysis of 2 and 3 readily proceeded in a benzene solution to yield quantitative amounts of MeSiPh(3) as the reductive elimination product. Kinetic studies on the thermolysis of cis-2 revealed that the reductive elimination is predominantly initiated by dissociation of the PMePh(2) ligand and accelerated by acetylenes and olefins added to the system.