An image forming apparatus and an auto color registration method thereof. The image forming apparatus performs an auto color registration (ACR) operation by excluding or minimizing the influence caused by variation in speed of a drive unit driving a transfer member. The image forming apparatus includes a controller, which prints a test pattern of each color according to a rotation period of the drive unit, and controls an operation for outputting an image in which each color registration error is corrected on the basis of the test pattern, such that a reliability of the ACR operation is increased and a quality of an image output from the image forming apparatus is also increased.