The present invention discloses an apparatus and method for deciding an access system based on WLAN signal strength in a WLAN/mobile phone network interworking system, and a mobile terminal therefor. The method for deciding the access system based on the WLAN signal strength in the WLAN/mobile phone network interworking system includes an initialization step for performing an initialization process on a WLAN driver module and a mobile phone network driver module, and measuring and displaying WLAN signal strength, a service decision step for selecting a WLAN service or mobile phone network service according to the measured WLAN signal strength, and a service access step for enabling the corresponding driver module to access the service decided in the service decision step. The apparatus and method for deciding the access system based on the WLAN signal strength provide a roaming service by efficiently interworking a WLAN which provides a high speed internet access service based on hot spots and a mobile phone network which provides a national communication service, to facilitate activation of the wireless internet service.