An image forming apparatus and a method of controlling power-saving modes of the image forming apparatus are provided. The method of controlling power-saving modes of the image forming apparatus includes beginning a first power-saving mode after standing by in a normal mode for first time if no print operation is implemented, and beginning a second power-saving mode after standing by in the normal mode for second standby time if an error occurs under implementation of a print operation, wherein the second time is shorter than the first time, and the second power-saving mode includes a an error-checking mode.