The present invention relates to a method and system for providing voice-based supplementary information service using road map data. The voice-based supplementary information service system includes a content registration server for receiving content for the voice-based supplementary information service, and converting the content into supplementary information data having voice data format. At least one GPS satellite detects a location of the mobile communication terminal and transmits GPS radio waves, including the location information. A mobile communication terminal receives the location information and requests the road guidance service and the supplementary information service. A relay server relays requests for the road guidance service and the supplementary information service. A road search server generates road map data and transmits the road map data to the relay server. A user management server determines whether the request for the supplementary information service exists in the road map data. An information provision server verifies the type of supplementary information service, receives supplementary information data corresponding to the type from the content registration server, and generates supplementary information-added data in which the supplementary information data is included in a data area of the road map data.