The aim of this work was to investigate a Ru-cluster material with a low molybdenum concentration. This latter is considered to act as an adsorption site for molecular oxygen. Transition metal chalcogenide materials based on Mo-Ru-Se for electrocatalytic reduction of molecular oxygen in acid medium were chemically prepared by reacting the transition metal carbonyl compounds and selenium powder in xylene solvent (140 degrees C). The stoichiometry of the semiconducting electrocatalyst corresponds to (Ru1-xMox)(y)SeOz where 0.02 < x < 0.04; 1 < y < 3 and z approximate to 2y. Kinetics parameters were obtained using steady state measurements with the rotating ring disk electrode (rrde) with electrocatalyst deposited on glassy carbon disks or with the powder incorporated in a disk of carbon paste matrix. Oxygen reduction proceeds mostly via a four-electron transfer reaction (96%) to water as determined by the rotating ring disk electrode technique. The heterogeneous rate constants, k(1) (water formation from oxygen), k(2) (hydrogen peroxide formation) and k(3) (water production from generated H2O2) were evaluated over the potential range of 0.70 to 0 V/nhe. Temperature dependence (296 K to 338 K) and kinetic parameters were evaluated It is concluded that minimising the molybdenum content leads to improved electrocatalysis.