Abstract: A vehicle theft prevention service method and system is capable of estimating theft of a vehicle even in the case where such a two-wheeled vehicle can be moved without start-up to be stolen and a vehicle theft prevention service method and system where a user is informed of location of a vehicle at the time of estimating theft of the vehicle, so that it is possible to accurately determine the theft based on the location of the vehicle at the time of estimating the theft of the vehicle. The vehicle theft prevention service system includes an electronic key and a theft monitoring device. The theft monitoring device is installed in a vehicle and determines that the vehicle is in a theft-estimated state and transmits an alarm message if a sensed acceleration value obtained by sensing a movement of the vehicle is a predetermined value or more. The electronic key outputs an alarm if the alarm message is received. Herein, the external apparatus may be a user terminal or a server.