The present invention relates to a method, packet data network gateway (PGW), and server in a mobile communication system and device for controlling charging in a mobile communication system. The method by a PGW in a mobile communication system includes identifying data usage information associated with a specific service for a terminal, determining whether the data usage information satisfies a predetermined condition, and transmitting a notification message including the data usage information if the data usage information satisfies the predetermined condition, to a policy and charging rules function (PCRF) entity. The data usage information is used to display a message in the terminal.