An abnormality detecting apparatus for an air temperature sensor which can detect an abnormality of the air temperature sensor with high reliability. The determination of abnormality is performed based on a detected temperature of the air temperature sensor when it is determined that the engine is in a sufficiently warmed state and when it is determined that the vehicle is stopped. The determination may be performed based on a temperature detected by the air temperature sensor during a predetermined period after a start of the engine when the start of the engine is detected and when it is determined that the engine is in the sufficiently warmed state. Additionally, the determination may be performed based on a temperature detected by the air temperature sensor after detecting a start of a cooling fan.