Reduction of Ti(Ⅳ)-oxalate complex on dropping mercury electrode has been studied as a function of oxalate concentration and of pH varied with HCl. Assuming there are equilibrium $TiO(C_2O_4)_2= ;+;2H^+;=;Ti^{+4};+;2C_2O_4;=;+;H_2O,;K_4$ in addition to $TiO(C_2O_4)_2;^=;=;TiO^{++};+;2C_2O_4=;K_2;Ti(C_2O_4)_2;^-;=;Ti^{+3};+;2C_2O_4=;K_3$ in the system cathodic wave has been well explained for that pH is higher than 0.5. The equilibrium constants $K_2,;K_3$ and $K_4$ have been to be $2{ imes}10^{-12},;5{ imes}10^{-13}$ and $10^{-11}$, respectively. The reduction of Ti(Ⅳ)-oxalate system is $Ti^{+4};+;e;{ o};Ti^{+3}$<TEX> in the concentration of hydrochloric acid, higher than 3M.