PURPOSE: To obtain thin foil by using a rolling mill of a low speed and low horsepowder by specifying the kinematic viscosity of a rolling mill lubricant to be supplied to rolling rolls and specifying the length at which the ends on both sides of the rolling part of a thin sheet material project from the side ends of the thin sheet material.

CONSTITUTION: The prescribed thin metallic sheet is passed through the rolling mill at a low speed below 50m/min and is rolled by the mill to the prescribed thin foil. The rolling mill lubricant having 6.0W15.0 centistokes kinematic viscosity at 40°C is used as the rolling mill lubricant to be supplied to the rolling rolls in this case. The thin sheet material rolling parts of the rolling rolls are positioned in the central part of the rolling rolls and the length of the rolling parts in the axial central direction of the rolling rolls is determined at such a size at which the ends on both sides thereof project respectively by 10W75mm from the ends of the thin sheet material.