This work has investigated the electrochemical properties and kinetics on the reduction of uranium(VI) at titanium electrode in a simulated solution of nitric acid and hydrazine. The analysis of a system with the electro-reduction and the mass transfer of uranium(VI) from organic phase was simulated by a model. The reduction of uranium(VI) needed a very high activation overpotential at non-pretreated titanium electrode in nitric acid and non-neutralized hydrazine media. It was affected by the ratio of hydrazine mono-hydrate to nitric acid rather than by only absolute amount of hydrazine mono-hydrate. When the above ratio exceeded 0.5, the reduction current decreased rapidly due to decrease of solution conductivity and increase of iR drop which were caused by consuming proton in the solution by the hydrazine mono-hydrate. There is less effect on the uranium reduction by the hydrazine mono-hydrate when the ratio is less than 0.5. The reduction of uranium(VI) was governed by charge-transfer controlled mechanism. It also was totally irreversible below potential showing a limiting current in current-potential curves. The experiment was performed for the neutralization of hydrazine mono-hydrate by nitric acid at pH 4.25. The reduction peaks of uranium(VI) of the voltammograms measured by electrochemical non-pretreated titanium electrode was not clear enough to be used for the kinetic analysis of the reduction of uranium(VI). The existence of oxide film at the titanium electrode without non-electrochemical pretreatment was confirmed by EPMA and a chronoamperometry method. The oxide film was effectively removed by a cathodic polarization method. The time for the removal of the oxide film, $t_{pr}$, depended only on a supplying electrolytic potential, $E_{pr}$. $$t_{pr} = 15.8E_{pr}\,^{-3.1}(-0.55\le{E_{pr}}\le{-0.9}\;V)$$ The electrode pretreated by the cathodic polarization gave good reduction peaks of uranium(VI) in the voltammogram by which kinetic analysis could be done. Because the reduction peak current at the pretreated titanium electrode in the nitric acid- neutralized hydrazine media was higher and was shifted to positive direction from the hydrogen evolution region than one at non-pretreated titanium electrode, the more effective system efficiency could be gotten. The reduction of uranium(VI) was found to satisfy the characters of irreversible electroreaction well. It was found that the ordinary electrolytic polishing method should not be applied to this titanium electrode, because even week positive potential produced strong oxide at the titanium electrode. The reduction of uranium(VI) depended strongly on nitric acid concentration. At more than 3 M nitric acid, the reduction peaks of uranium(VI) of voltammograms were overlapped with the currents of vigorous side reaction of hydrogen evolution or the reduction of nitric acid. Hence, the peak analysis was not possible. The existence of hydrazine in the solution was important in the uranium reduction because of preventing the reoxidation of uranium(IV), but the concentration of hydrazine had no effect on the uranium reduction. The hydrazine concentration of 0.1 M was enough to prevent the reoxidation of uranium(IV). A possibility was found that a uranous hydroxide was adsorbed at the titanium electrode in nitric acid of less than 0.75 M and it hindered the electro-reaction. The kinetic parameter, $\alpha\mbox{n}_a$, depended on nitric acid but the k$_0$ didn't. The following electro-reduction rate constant was obtained $$k_f = A \exp\{ - [B+C ln(C_{HNO_3})]F/RT[E_{app} - E^{0'}]\}$$ where, A, B, C, and $C_{HNO_3}$ are $5.659\times10^{-8}$, 0.111, 0.021, and the concentration of nitric acid (M), respectively. The controlled-potential of -0.5 V(vs. SSE) was suitable to the electrolysis operation for the production of uranium(IV) at titanium electrode with the best current efficiency and safe operation. A model for an analysis of the mechanism of electro-reduction accompanying mass transfer of uranium(VI) was set up on the basis of the two film theory. It was found that an optimal nitric acid concentration existed in terms of maximum production rate of uranium(IV) in a given time. The produced uranium(IV) culminated at near 0.3 N of nitric acid and then decreased rapidly. The mass transfer depended on more strongly the production rate of uranium(IV) rather than the electroreduction. The composition of uranium(IV) in a final solution depended strongly on the electrode area, but little on the mass transfer area. It was recommended for the maximum production rate of uranium(IV) that the nitric acid concentration should be kept as low as possible, but more than 0.5 N. The optimal electrode areas were be estimated from the simulations, when production yields of uranium(IV) and production compositions of uranium(IV) were decided to meet specific conditions for the separation of uranium and plutonium in PUREX process and the production of uranium(IV) in two phase system, so on.