Highly dispersed, oxide- or zeolite-supported bimetallic catalysts are widely used in the catalytic industry, such as in catalytic reforming, nitrogen industry and gas-to-liquid technology. The paper highlights the nano-sized Co-based bimetallic system in terms of correlation between structure and reactivity/selectivity promoted by the second metal. Opposite to the bulk alloys nano-sized bimetallic catalysts are extremely sensitive to the structure, morphology, valence state of the supporting oxide material in which the nano-particles are embedded. In this case, one of the less reducible components, which strongly interact with the supports, may stabilize the second, more noble metals, and thus the latter can be stabilized in highly dispersed state. Conversely, addition of noble metal to the hardly reducible component may facilitate reduction, which causes the retardation of the deactivation process of some hydrocarbon reaction. The future trend is the application of bimetallic nano-particles although careful consideration and experimentation should be taken to elucidate the structure of such type of catalyst. The various effects of Co-based bimetallic particles, such as particle size, metal/support interface, morphology and electronic effects, on the activity/selectivity in given catalytic reactions will be discussed.