A family of novel catalysts for oxygen electroreduction is presented, based on nanostructured RuxXy chalcogenide compounds (X = S, Se, Te). EXAFS data suggest that the catalysts have a core of ruthenium atoms, which has triangular co-ordination and a direct metal-metal bond. Depending on the chalcogen, the Ru-cluster consists of two or three metal layers of different size and mutual co-ordination with chalcogen atoms co-ordinated to the periphery of the cluster. Variation of the chalcogen type affects the size of the Ru-cluster and the strength of its interaction with the chalcogen. This influences the interaction of Ru-clusters with oxygen and thus their activity in the reduction of molecular oxygen.