In this paper, we investigate the performance of the twoway decodeandforward (DF) relaying system with automatic repeat request (ARQ) protocol in Rayleigh fading channels. In the proposed ARQ scheme, the ARQ process is carried out by all of the nodes including two source nodes and a relay node which have the buffers to store the signals received from different slots. In order to make full use of the received signals in diffident slots, MMSE signal detection and maximal ratio combining (MRC) are used in the protocol where retransmission are requested according to different conditions and nodes. In addition, simulation results show that the proposed protocol can improve the packet error rate (PER) and spectral efficiency of the DF based twoway relay system than the conventional ones.