A radio communication system and transmission method using Multi-Radio Access (MRA) interfaces are provided. The radio communication system and method include a transmitter and a receiver having at least two Radio Access (RA) interfaces capable of communicating through different frequency spectrums, in which each of the transmitter and the receiver includes a multiple radio transmission layer for activating a multiple radio transmission entity for each upper layer service and transmitting data in packet units and an RA layer for activating at least one RA entity that manages the RA interface for the multiple radio transmission entity and dividing a packet into sub-packets for transmission and reception. In the transmission method, the multiple radio transmission entity of the transmitter receives a packet transmission success indicator for a specific packet from the RA entity of the transmitter and a next packet is transmitted upon receipt of the packet transmission success indicator. In the transmission method, a link having a good channel status is selected as a retransmission channel according to the status of an RA link of the lower layer, thereby allowing efficient and rapid data transmission.