Abstract: Disclosed are a system and method of issuing a key for a door lock at lodging facilities using a smart phone, wherein the system includes: a guest smart phone that makes a request for a reservation and payment at lodging facilities; a door-lock key issuing server that is requested to make a reservation and payment from the guest smart phone, acts as a proxy to make the reservation and payment at the lodging facilities; and a lodging-facilities server that approves the reservation and payment made by the door-lock key issuing server, receives the password of the key for the door lock from the door-lock key issuing server, approves the smart phone when accessed by the smart phone, and permits the door to be open by the Bluetooth communication with the approved smart phone.