Abstract: A resource allocation algorithm based on effective capacity theory for downlink multi-service OFDMA systems is proposed, which is focused on the real-time users QoS requirements. A two-dimensional Markov wireless channel model is established, and the radio resources are allocated to real-time users by the adaptive modulation technology, the effective capacity theory and the effective bandwidth theory. The downlink radio resources are also simultaneously allocated to non-real-time and best effort users appropriately. Simulation results show that the proposed algorithm ensures the throughputs of the downlink OFDMA systems, meanwhile, it has some advantages on delay and packet dropping rate of real-time users.