A lens module with auto-focusing mechanism includes a plastic lens barrel, a lens assembly, an auto-focusing mechanism and a coil regulating structure. The plastic lens barrel includes a front end portion, a rear end portion and an outer side portion, wherein the front end portion includes a front end surface and a front end hole, the rear end portion includes a rear end opening, the outer side portion connects the front end portion and the rear end portion. The lens assembly is disposed in the plastic lens barrel, and includes a plurality of lens elements. The auto-focusing mechanism is connected to the plastic lens barrel, and includes a coil being polygon. The coil regulating structure is located on the outer side portion of the plastic lens barrel, and is integrated with the plastic lens barrel, wherein the coil is connected and positioned to the coil regulating structure.