An imaging lens system includes a plastic lens element, a lens barrel and a light-absorbing coating layer. The plastic lens element is accommodated in the lens barrel and has an outer annular surface. The lens barrel includes a plate portion and a lateral wall portion. An optical axis of the imaging lens system passes through a light-passable hole of the plate portion. The lateral wall portion is connected to the plate portion and extends along a direction substantially parallel to the optical axis. The light-absorbing coating layer has an inner surface and an outer surface. The inner surface faces and is fixed on the outer annular surface of the plastic lens element. The outer surface is located opposite to the inner surface and in physical contact with the lateral portion of the lens barrel.