This invention relates to a copper alloy for reliable electrical connection comprising 0.5-3.0 wt% preferably 0.6-2.3 wt% of Co, 0.03-0.4 wt% preferably 0.06-0.35 wt% of P and the balance being composed of Cu and unavoidable impurities contained in electrolytic copper, and furthermore relates to a reliable connecter and a reliable connecting method using a copper alloy thereof.