The present invention is related to transmitting data in a mobile communication system. Preferably, the present invention comprises transmitting first data to a receiving side and receiving acknowledgment information for indicating whether the first data was successfully transmitted to the receiving side. If the first data was not successfully transmitted to the receiving side, the method further comprises determining whether an amount of available radio resources is sufficient for retransmitting the first data to the receiving side, retransmitting the first data to the receiving side if the amount of available radio resources is sufficient to retransmit the first data, reconfiguring the first data into at least one second data if the amount of available radio resources is insufficient to retransmit the first data, wherein the at least one second data can be transmitted to the receiving side using the amount of available radio resources, and transmitting the at least one second data to the receiving side.