To provide an electrolytic copper foil which has high normal tensile strength and whose tensile strength is hardly deteriorated after thermal history, in regard to an electrolytic copper foil used as a negative electrode collector for a lithium ion secondary battery.

An electrolytic copper foil is produced by using a sulfuric acid-based copper electrolytic solution containing glue in an amount of 6-11 ppm by mass and performing electrolysis at a ratio to limiting current density of 0.14-0.16 to make electrodeposition onto a rotating cathode drum made of titanium or stainless steel. The electrolytic copper foil has a normal tensile strength of 500-750 MPa and a tensile strength of ≥350 MPa after heating at 400°C for 1 hour.