Abstract: Ad hoc networks attract a considerable attention due to their simplicity, low cost and efficiency. Using multimedia applications on these networks will be more widespread in the future. In contrast with best-effort flows, real-time ones seriously need Quality of Service (QoS) support. This study proposes a completely distributed algorithm to provide QoS in ad hoc networks. The proposed algorithm, entitled Light Weight distributed QoS Algorithm (LWQA), using queue data structure and linear algebra, dynamically adjusts Contention Window (CW) related to the flows. Furthermore, LWQA utilizes static or low speed nodes during routing of real-time flows to increase their QoS. In addition to considering flows’ priorities, the proposed algorithm is able to distinguish between flows of the same type. We proved the correctness of this algorithm using markov’s mathematical model and implemented it in a simulation environment using the Network Simulator Version 2 (NS-2) Software. The simulation results demonstrate that LWQA improves the QoS in ad hoc networks.