A method and system of preventing a loss/theft using a wireless personal area network (PAN) or a wireless local area network (LAN) which can receive, from a mobile device included in a surveillance target via a gateway, a location information of the surveillance target generated by using mobile device information for the surveillance target, the mobile: device information being collected by a; sensor of the mobile device, and signal information communicated between the mobile device and a fixed device, can determine whether there is a loss or a theft by comparing surveillance target information and a permission standard, and can provide alert information including the location information of the surveillance target when there is the loss or the theft is provided.