The present invention relates to an accounting method and an accounting apparatus in a mobile communication system. The amount of radio resources and traffic used by a mobile terminal of each subscriber accessing a base station can be measured and analyzed without changing a structure of the mobile communication system. In addition, since a provider who does not own an IP network and thus uses a leased network of an existing provider can measure and analyze the amount of traffic used by a mobile terminal in the leased network regardless of an IP network of the existing provider, a more precise accounting reference can be provided to the corresponding provider.