The kinetics of the [Mn(CN6]4- + e- half arrow right over half arrow left [Mn(CN)6]5- system at mercury electrodes has been investigated using cyclic voltammetry, chronocoulometric and faradaic impedance methods. The standard heterogeneous rate constant k(s) of this process in 1 mol dm-3 NaCN is 0.26 +/- 0.015 CM s-1 and the cathodic transfer coefficient alpha is 0.59 +/- 0.01, similar to the kinetic characteristics of the [Cr(CN)6]3-/[Cr(CN)6]4- system. The diffusion coefficient of [Mn(CN)6]4- in 1 mol dm-3 NaCN is (5.6 +/- 0.8) X 10(-6) cm2 s-1. The role of the composition of the inner coordination sphere of manganese complexes in their electroreduction mechanism and the possibility of the further electroreduction process [Mn(CN)6]5 + e- --> [Mn(CN)6]6- at mercury electrodes are discussed using literature data.