The present invention relates to a wireless communication system, and more particularly, discloses a method and an apparatus for transmitting and receiving duplicate data in a multicarrier wireless communication system. According to one embodiment of the present invention, a method in which a transmitter, which supports carrier aggregation for performing communication using N (N≧2) component carriers, transmits duplicate data, comprises the steps of: generating, in a media access control (MAC) layer of the transmitter, N duplicate data using radio link control (RLC) protocol data units (PDUs) from an RLC layer, and simultaneously transmitting, to a receiver, the respective N duplicate data on the N component carriers through respective N hybrid automatic repeat and request (HARQ) entities.