Due to the advancement in the Information Technology, different kind of companies with heterogeneous needs have had the necessity to cooperate among them to get more benefit in a continuos changing market. That is heterogeneous e-business. In order to cope with such kind of e-business, a platform which can effectively realize heterogeneous needs, real time, flexibility and fault-tolerance is needed.This paper focuses on the database field that is indispensable for the e-business. Thus, it proposes Autonomous Decentralized Database System, which is composed of two techniques. In the first one, the concept of Allowable Volume (AV) is introduced, while in the second one, a Mobile Agent (MA) that adjusts the AV of each site is shown. Since the MA is always moving among the sites, and each site can always negotiate AV with the MA autonomously, the system can realize assurance. Furthermore, the effectiveness of the proposed system is shown by simulation.