This paper proposes an improved dynamic bandwidth allocation algorithm for dual Quality of Service (QoS) classes to maximize the utilization rate of the Resilient Packet Ring (RPR). To achieve dynamic bandwidth allocation for the two QoS classes in the RPR, each node measures the high priority traffic flow and assigns the appropriate bandwidth; the remaining bandwidth is used for low priority traffic. It passes a control frame containing the measured bandwidth of the high priority traffic to the other nodes. Based on the advertised high priority traffic bandwidth, any node that is congested transmits, to the other nodes, a fairness message to fairly allocate the remaining low priority bandwidth. Simulations demonstrate that the proposed algorithm enhances the utilization rate and reduces the delay of high priority frames.