A process for manufacturing a gas sensor, the gas sensor including a gas detecting element, cylindrical metal shell, and cylindrical protector as defined herein, the process comprising: applying a lubricant to an outer circumference of a leading end portion of the metal shell; assembling the metal shell having the lubricant applied thereto and the protector, so that a fitting portion, in which the leading end portion of the metal shell and the protector fit on each other, and a space-forming portion, in which the leading end portion of the metal shell and the protector overlap each other through an annular space, are formed along an axial direction; and welding the metal shell and the protector by forming a welded portion extending from an outer circumference of the protector through the annular space.