A method and apparatus is provided for signaling network sharing information about neighbor cells in an NS system where a RAN is shared among a plurality of CN operators. In the signaling method, it is determined whether each of neighbor cells of a current cell in which a UE is located, is shared by a CN operator other than a CN operator controlling the neighbor cell. System information without network sharing information is generated if at least one of the neighbor cells is shared by a CN operator other than a CN operator controlling the neighbor cell. System information including the network sharing information is generated if none of the neighbor cells are shared by any CN operator other than CN operators controlling the neighbor cells. The system information is then broadcast to the UE from the current cell.