A proximity sensor includes a transmitter unit, a receiver unit, and a housing. The transmitter unit transmits a light signal. The receiver unit receives the light signal reflected by an object to determine a proximity status of the object. The housing defines a first enclosed accommodation space for accommodating the receiver unit, wherein the portion of the housing defining 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.