Smartphones and sensor devices have come into widespread use, and we can observe huge amounts of data from the devices via the Internet. In order to develop a network application which uses these devices effectively, we need an accurate and scalable data aggregation mechanism. In this paper, we propose a accurate data aggregation mechanism which is based on a scalable structured p2p network. The proposed mechanism is constructed by two concepts: Asynchronous Data Aggregation and Time-slot-based Data Aggregation. In the proposed mechanism, the amount of communication data required for data aggregation is O (log N), where N is the number of nodes. Additionally, the proposed mechanism achieves accurate data aggregation even if the structured p2p network is unstable. In this paper, we explain an algorithm and a communication protocol for the proposed data aggregation mechanism. Furthermore, using experimentally obtained results, we indicate advantages of our proposal over existing data aggregation mechanisms.