Voltammetry of U(VI) at graphite electrodes in aqueous media containing magnesium chloride electrolyte consists of two chemically reversible major processes within the pH range 2.4 to 6.6. The dominant process at low pH is observed in the potential region of about 0 to - 0.3 V (vs. SCE) under conditions of cyclic voltammetry and is assigned to the reaction UO22+(aq) + e- --> UO2+(aq) <--> UO2+ (adsorbed) This process is progressively replaced by another response over the potential range-0.6 to -0.8 V (vs. SCE) as the pH is increased and UO22+ is hyrolyzed to [(UO2)x(OH)y](2x-y)+. The second process is also a U(VI)/U(V) process represented by the equation [(UO2)x(OH)y](2x-y)+ + e- <--> [(UO2)x(OH)y](2x-y-1)+ Interestingly, many of the characteristics of the second process are closely related to reduction of solid uranium oxide compounds, such as U3O8, alpha-UO3 and gamma-UO3, mechanically attached to graphite electrodes, where diffusion of inserted magnesium ions from the electrolyte, rather than diffusion of solution soluble U(VI) complexes, provides the mass-transport mechanism. The fact that similar reversible U(VI)/U(V) reduction potential and voltammetric characteristics are observed for solid oxides and hydrolyzed forms of UO22+ suggests that common features of the electron transfer process occur in all of the basic forms of U(VI). Voltammetric reduction of U(VI) compounds at graphite electrodes in magnesium chloride electrolyte seems to be inherently simpler than reported at other electrodes in that it is dominated by chemically reversible U(VI)/U(V) electron transfer processes.