The invention relates to a nipple sterilizer which may easily sterilize the nipple of a nursing bottle. According to an aspect of the invention, there is provided a nipple sterilizer comprising a body 10 which has an opening 12 at its lower surface and is to be mounted at a nursing bottle 2 in order that the nipple 6 of the bottle 2 may be inserted through the opening 12 and may be covered thereby, a sterilization lamp 20 which is positioned inside the body 10 and sterilizes the nipple 6, an electric power source 30 which is positioned inside the body 10 in order to be connected to the sterilization lamp 20, a switch 40 which is electrically connected between the electric power source 30 and the sterilization lamp 20 and makes the sterilization lamp 20 switched on and off.