An image forming apparatus having a file-format conversion function and a method thereof. The image forming apparatus is capable of performing a data communication with an external memory device. The image forming apparatus includes an interface unit to receive a first file from the external memory device and to transmit a second file to the external memory device, and a file converter to convert a format of the first file from a first format into a second format according to information on the first and second files. Thus, the format of the received file can be converted in the image forming apparatus in a simple and speed way.