Abstract: Diabetes Mellitus is a metabolic disorder affecting carbohydrate metabolism, metformin is a drug widely used in the treatment of this disease. However, its mechanism of action has not been know yet, although several theories have been proposed to explain its hypoglycemic activity. A recent theory suggests a relationship between metformin and mitochondrial copper. On the other hand, glucose is the most abundant carbohydrate working as energy source; this carbohydrate has an important role in Diabetes Mellitus. In the present research work is reported a UV-VIS study with the purpose of analyzing the in vitro interaction between the ionic copper, metformin and glucose or mannose. The formation constant of ternary complexes of copper with metformin and glucose or mannose and its calculated electronic spectrum of each species in methanol solution, are reported. Hopefully, this information can be used in order to predict some of the possible interactions in vivo.