The present invention relates to a method and apparatus for transmitting and receiving data in a multi-carrier communications system. The data transmission/receiving method uses multiple carriers including a primary carrier that is capable of transmitting and receiving data traffic and PHY/MAC control information between a terminal and a base station and at least one secondary carrier that transmits and receives down-link data traffic between the terminal and the base station. The method comprises: generating an MPDU (MAC Protocol Data Unit) to be sent to a PHY (Physical) layer in an MAC (Medium Access Control) layer; performing channel-coding and modulation on the MPDU to generate a modulated symbol sequence in the PHY layer; segmenting the modulated symbol sequence into multiple symbol sequences; and allocating the multiple segmented symbol sequences to multiple carriers, respectively, to perform IFFT (Inverse Fast Fourier Transform) and transmit to a terminal, wherein control information on the multiple carriers is allocated to a control channel region of the primary carrier and transmitted via the primary carrier.