A novel binuclear Pt(III) complex, Pt-2(dtp)(4)Br-2 (dtp = CH3CH2CS2-, dithiopropionato), was synthesized by a reaction of Pt-2(dtp)(4) and Br-2 in refluxing toluene, which could be used as starting material for a new MMX-chain system such as a possible mixed-valence Pt-2(dtp)(4)Br. The title complex has been characterized by X-ray single-crystal structure analysis, UV-Visible-NearIR, IR, and polarized Raman spectroscopies. The Pt-2(dtp)(4)Br-2 crystallized in monoclinic P2(1)/a and this structure is almost same as Pt-2(dtp)(4)I-2. Halogen-replacement effect from X = I to Br on Pt-2(dtp)(4)X-2 has been examined. The Pt-Pt distance in X = Br is slightly shorter than that in X = I. Raman peak of the v(Pt-Pt) mode is slightly shifted to higher wavenumber from X = I to Br. These changes are considered to be mainly caused by the difference of electron densities of antibonding d(sigma)* orbitals.