We have found that an exclusively cathodically pretreated glassy carbon electrode, which has been hitherto considered ineffective in many redox systems, is highly activated towards monomeric Mo(VI) adsorption and its reduction. The most commonly used anodic pretreatment produces an inactive GCE surface with poor response. X-ray photoelectron spectroscopy has been used to probe the surface concentration change of O- and C-containing species with the pretreatment, and identify the nature of the molybdate species adsorbed on the pretreated GCE surfaces. The results obtained clearly show that the precathodisation produces > C-O-surface groups, and that there is a correlation between the saturation surface coverage of Mo(VI) determined by cyclic voltammetry experiments and the alcohol O/total O ratio of the pretreated electrodes calculated from XPS measurements. The unusual activation by precathodisation is explained by a mixed potential mechanism.