A method and a device for selecting a cell in a mobile communication system and for selecting a cell for transmitting data, by a base station, not only in a licensed frequency band but in an unlicensed frequency band. A method for configuring a cell of a base station includes connecting with a terminal through a first cell of a licensed band; transmitting, to the terminal, a message for configuring multiple second cells in an unlicensed band through the first cell; and monitoring the configured multiple second cells in the unlicensed band, wherein the number of the multiple second cells exceeds the number of cells, a carrier aggregation of which the terminal can support. The present disclosure relates to a 5G or a pre-5G communication system to be provided in order to support a higher data transmission rate after a 4G communication system such as an LTE.