Nanocomposite polymer films of [Ru(bpy)2(PVP)10] 2+ metallopolymer and gold monolayer-protected clusters (MPCs) have been formed. Cyclic voltammetry of the films has been performed in both acidic (0.1 M H2SO4) and neutral (0.1 M Na2SO 4) pH electrolyte solution. In acidic electrolyte, the protecting monolayers is desorbed as the gold surface is oxidized. Transmission electron microscopy of the nanocomposite following electrochemical cycling reveals aggregates of "naked" MPCs. In sharp contrast, in neutral pH electrolyte, the MPCs are stable towards voltammetric cycling and no gold oxide formation is evident in the voltammetry. The homogeneous charge-transfer diffusion coefficient, DCT, was determined for a range of nanocomposite films as the MPC mole fraction is systematically varied. When acidic electrolyte is used, DCT decreases from 2.8 ± 0.5 × 10-10 to 1.5 ± 0.1 × 10-11 cm 2 s-1 as the MPC mole fraction is increased from 0 to 0.45. In contrast, the DCT determined in neutral electrolyte is universally lower than that determined in acidic electrolyte, it increases by over two orders of magnitude from 2.6 ± 0.9 × 10-15 to 4.0 ± 0.5 × 10-13 cm2 s-1 as MPC mole fraction increases from 0.05 to 0.5. © 2011 Elsevier B.V. All rights reserved.