A boot Read-Only Memory (ROM) update method and a boot-up method of an embedded system are provided. The boot Read-Only Memory (ROM) update method of an embedded system including a memory and a ROM. The memory includes a user data area and a boot ROM area that includes a first area and a second area. The ROM copies a first boot code from the boot ROM area during boot-up. The boot ROM update method includes writing a second boot code to the second area in response to a first ROM update command. The second boot code includes a second boot ROM image and a second signature for the second boot ROM image. The method also includes verifying validity of the second signature and, if the second signature is valid, swapping the first area and the second area. The first boot code is disposed in the first area and includes a first boot ROM image and a first signature for the first boot ROM image.