In this paper, we propose a dynamic channel assignment (DCA) scheme for distributed antenna networks (DANs). DANs, in which many antennas are distributed in each cell, significantly reduce the transmit power compared to conventional cellular networks (CNs). In DAN, a different group of channels should be assigned for each distributed antenna to avoid the interference. Since DAN can also reduce the interference power due to its low transmit power property, the same channel groups can be reused even within the same cell. Proposed DCA scheme dynamically assigns the channels based on the co-channel interference measurement. Computer simulation results demonstrate that the DAN using proposed DCA achieves higher spectrum efficiency than the conventional CN.