A novel pentacyano complex of trivalent platinum dimer, [(CN)₅Pt-Pt(CN)₅]⁴⁻, stabilized by Cu²⁺, has been prepared successfully on the electrode surface, by continuous cyclic potential scanning in a solution containing 3×10⁻³ M K₂Pt(CN)₆+3×10⁻³ M CuCl₂+1 M KCl. The applied potential is between 700 and −800 mV at a scan rate of 100 mV s⁻¹. The mechanism for the electrodeposition has been discussed. The film prepared displays an electrochemically inert characteristic and the deactivation effect of the film on the surface of GC electrode has been studied. Several surface analytic techniques, such as scanning electron microscopy (SEM), energy dipersive X-ray spectroscopy (EDAX), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF–SIMS), have been used to characterize the film. The results show that the ratios of N/Pt and Cu/Pt in the film are 5 and 1, respectively, and Pt in the film displays an identical oxidation state, which is between 2+ and 4+ according to the values of the binding energy. All evidence confirms the structure of the film as Cu₂[(CN)₅Pt-Pt(CN)₅]. The binuclear species [(CN)₅Pt-Pt(CN)₅]⁴⁻ is a rare representative of unbridged dimeric complexes of a trivalent platinum compound. This is the first time such a dimeric compound of trivalent platinum has been generated electrochemically.