A power saving system for a computer incorporating a standby power source includes a setting module, a detecting module and a controlling module. The setting module communicates with the BIOS of the computer and is configured for setting power saving modes on an interface provided by the BIOS for at least one function circuit, during the time the computer powered on. The detecting module is configured for detecting “enable” and/or “disable” signals output from the BIOS. The controlling module includes at least one switching circuit configured for correspondingly interrupting the power supply from the standby power source to one or more of the at least one function circuit after the computer is shut down and the detecting module receives “enable” signals.