The transfer behaviour of the heteropoly anion [SiW₁₂O₄₀]^4– across the water/nitrobenzene interface has been investigated using cyclic voltammetry and chronopotentiometry with cyclic linear current scanning. It was found that the heteropoly anion with a negative charge of 4 can transfer from the aqueous phase to the organic phase electrochemically. The transfer process is diffusion-controlled at a lower scan rate, but it is partially kinetically controlled at a higher scan rate. The effects of some higher-valent cations such as Sr²⁺, Co²⁺, Ni²⁺, Zn²⁺, Fe²⁺ and Fe³⁺, as well as some anions such as NO^–₃, Cl^–, SO^2–₄ and PO^3–₄etc. on the phase transfer have been systematically observed from cyclic voltammograms. The formal transfer potential and the transfer free energy for the heteropoly anion across the water/nitrobenzene interface have been calculated according to the voltammetric data.