Abstract: In mobile database systems, new features such as mobility, disconnection and long-lived transactions make traditional transaction processing schemes no longer suited. To solve this problem, a new mobile transaction model, O2PC-MT, is proposed in this paper. The O2PC-MT combines optimistic concurrency control with two-phase locking in mobile transaction processing, and utilizes two-phase commit protocol for the global commitment of mobile transactions. In this way, the O2PC-MT provides an effective support for the long-lived transaction property. In addition, mobile computers are allowed to submit mobile transactions in multiple request messages and to move arbitrarily during transaction execution. Therefore, the O2PC-MT provides a flexible support for interactivity and arbitrary mobility. The experiment results show that the O2PC-MT model outperforms the previously proposed mobile transaction models that utilize the two-phase locking or its variants for mobile transaction processing.