RED-RT is proposed to protect real time traffic from non real time traffic in routers. Active Queue Management (AQM) mechanisms in routers have been developed to prevent congestion and to improve the fairness between adaptive (TCP) traffic and non adaptive (UDP) traffic. But they do not consider the QoS requirements of flows. Real time traffic is usually transported via RTP over UDP. UDP traffic is not protected from dropping and even discriminated against TCP traffic. As a result, for real time traffic protection scheduling mechanisms are normally used. However, AQM can roughly satisfy the QoS requirements of real time traffic by classification of traffic into real time flows and non real time flows and by applying different policy to them. The proposed RED-RT does not drop real time traffic during non congested periods and applies a lower drop rate for real time traffic than that of non real time traffic during congested periods in a router. The simulation result shows that RED-RT can roughly satisfy the QoS requirements for bandwidth, drop rate, and delay for real time traffic. This means that RED-RT can be used as congestion control and preliminary substitution for scheduling mechanism for real time traffic.