A malfunction diagnostic apparatus for intake air temperature sensors includes a coolant temperature sensor; a first determination portion that determines that a precondition for performing a malfunction diagnosis is satisfied when a process of starting an engine is started, if a detected coolant temperature is determined to be equal to an intake air temperature detected by an intake air temperature sensor provided at a portion that is likely to be cooled, and a decrease amount, by which the detected coolant temperature decreases, is equal to or larger than a preset value; a second determination portion that makes a tentative determination based on a difference between the detected intake air temperatures, if the precondition is satisfied; and a third determination portion that determines whether the tentative determination is an invalid determination or a valid determination, based on a change in the detected intake air temperatures during a given time period.