A system and method for determining the time to change the oil of an automatic transmission includes: continuously tracing/storing oil change-related information, which serves as a basis for an oil change, from the point of time when new automatic transmission oil is provided, such as the point in time of a new car purchase or the point in time of an automatic transmission oil change; determining whether or not it is time to change the oil of the automatic transmission on the basis of the oil change-related information, a preset change reference value, an oil temperature reference value, a recommended vehicle travel mileage and the like. When it is determined to be the time to change the oil of the automatic transmission, an automatic transmission oil change signal is generated to inform a driver of the necessity of changing the oil of the automatic transmission.