Electrochemical methods have been used to study electron transfer reactions at the interface between an aqueous phase of less than 1 femto liters in volume and a bulk organic phase. The small aqueous phase is formed at the end of a slightly recessed platinum electrode. When a negative potential is applied between the Pt electrode and the aqueous phase, Ru(NH3)63+ in the aqueous phase could be reduced to Ru(NH3)62+. Because the volume of the aqueous phase is very small, the electrochemically formed Ru(NH3)62+ could instantly reach the interface between the aqueous phase and the organic phase which contains 7,7,8,8-Teteracyanoquinodimethane (TCNQ), and be oxidized to form Ru(NH3)63+ by giving electrons to TCNQ at the interface. Our results showed a positive shift in the E1/2 comparing the reaction undertaken in the recessed cavity and the bulk solution.