A keyboard illuminating device for a portable computer includes a battery module and an illuminating module. The battery module can supply power to the portable computer and includes a housing. The illuminating module is disposed on the battery module and is powered by the battery module to illuminate a keyboard of the portable computer. The illuminating module hides in the battery module when the keyboard illuminating device is in a first status, and the illuminating module protrudes from a surface of the battery module when the keyboard illuminating device is in a second status.