To provide an electrolytic copper foil with very smooth surface roughness on an electrolytic copper foil deposited surface, reasonable tensile strength at normal temperature in spite of very fine crystalline structure, high elongation, retaining stable strength without causing heat softening even after heat treatment, and having high elongation in high temperature atmosphere, and to provide the electrolytic copper foil for a current collector of a secondary battery having long charge-discharge cycles and preventing breakage even in overcharge.

The electrolytic copper foil suitable for the current collector of the secondary battery has such characteristics that the surface roughness on the electrolytic copper foil deposited surface has a minimum distance between peaks of material crests of 5 μm or less in spite of fine crystals smaller than 2.5 μm when the crystalline structure at normal temperature is represented by 10 point average roughness Rz, drop in normal temperature tensile strength after heat treatment at 130 °C for 15 hours is less than 15%, and heat softening is prevented.

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