Abstract: The polarization curves of copper physical development (CuPD) system were obtained by transient constant current step method on copper plated platinum electrode. The results showed that the cathode polarization curve for the reduction of Cu²⁺ and the anode polarization curve for the oxidation of BH₄^- have a crossing point, which corresponds to a mixed potential (E_mp) of -715 mV and a current density (i_R) of 8.9×10_-4 Acm_-2. These values are approximately the same as determined directly on the CuPD system, i.e. E_mp=-720 mV and i_R=8.7×10_-4 Acm_-2, respectively. This implies that the mixed potential approach is reasonable. In the CuPD system, there is little influence between the cathode reduction of Cu²⁺ and the anode oxidation of BH₄^-. When the electrode was coated with gelatin, the reaction rate was lowered, r=6.09 μgmin^-1cm_-2. This value is more approximate to the rate determined on the photographic layer, i.e. 4.82 μg min^-1cm_-2. The rate determined on clean electrode is much higher, 17.12 μg min^-1cm_-2. This showed the profound influence of gelatin on the physical development. The transfer coefficient a was obtained from the Tafel equation, and has a value of 0.48. This implies that the deposition of copper proceeds via two single electron transfer reactions, provided that the transfer of the first electron is rate-limiting.