The explosive demands of multimedia services have been grown up to support delay-sensitive applications, e.g., VoIP and streaming using codec. When a Mobile Node (MN) moves across different types of networks, the codec should be effectively adapted according to the significant change of network condition, i.e., throughput and delay. Therefore, in this paper, we propose A Codec Adaptation for Vertical Handover (ACAV), aiming not only to increase throughput but also to decrease delay at MNs. Using Media Independent Information Service (MIIS), the ACAV is able to proactively estimate network conditions of the target network then determine a proper type of codec for on-going multimedia services. The simulation results show that the proposed ACAV outperforms typical codec adaptation mechanism in terms of throughput and delay by determining a proper codec for the target network.