Light-trail (LT) has been proposed as an attractive solution for optical networks to support emerging services such as video-on-demand, pseudo-wires, data-centers, etc. Due to the fact that light-trail (LT) is a shared-medium network, the media access control (MAC) protocol is essential to be implemented in the whole network. In this paper, we propose a novel MAC protocol called DAART (Delay-aware Adaptive Round Time) to improve the throughput in LT network. DAART MAC adopts the delay-aware mechanism to calculate the actual token holding time for every transmission node. More specifically, the token holding time can be evaluated from queue delay, transmission delay and slot-synchronization delay. To estimate the throughput performance of DAART MAC protocol, we give three different patterns of traffic and compare the throughput between DAART MAC and ART MAC. Simulation results show that DAART has more stable throughput performance than ART, which in return enhances the throughput of LT networks.