Abstract: It is an object of the present invention to provide a copper alloy foil that achieves both electrical conductivity and heat resistance to solve the above-mentioned problem. It is another object of the present invention to provide a copper alloy foil that, when used for a negative electrode current collector of a secondary battery, exhibits improved adhesion to an active material layer. A copper alloy foil contains 0.005 to 0.015 wt % of Sn and has an oxygen content of 0.0020 wt % or less, the balance being Cu and inevitable impurities. A Sn-rich layer is formed on at least one surface layer of the copper alloy foil.