The electrochemical behavior of C-70 fullerene films on gold and glassy carbon substrates was studied in aqueous solutions. The neutral C-70 film behaved as an intrinsic semiconductor electrode, and it could be transformed to a conductor by electrochemical reduction. We observed that C-70 could be reduced in the presence of various cations, and the reduction process shifted parallel with the hydration Gibbs energy of the cations. In each case the reduction consumed about three electrons per C-70 molecule. The potential of the reduction changed with the activity of the cations, indicating the formation of some ion-exchanging transient species. The C-70 fullerene electrodes had good stability at ambient conditions.