A proximity sensor includes: a transmitter unit for transmitting a light signal; a receiver unit for receiving the light signal reflected by an object to determine a proximity status of the object; and a housing defining a first enclosed accommodation space for accommodating the receiver unit, wherein the portion of the housing which defines the first enclosed accommodation space has a sealed light passage made of a light-transmissible material such that the receiver unit is capable of receiving the light signal reflected by the object through the light passage. The housing can further include a second enclosed accommodation space for accommodating the transmitter unit.