The martensitic transformation was studied in a mechanically alloyed and then spark plasma sintered Cu-50 at.% Co alloy. The mechanical alloying of this alloy composition produced the formation of a supersaturated solid solution with nanometric grains. The martensite start temperature was determined to be below room temperature by means of electrical resistance measurements during cooling of sintered samples. The martensite start temperature decreased with the copper addition, compared to that of pure cobalt. Additionally, this temperature also decreased as the sintering pressure increased.