In this paper, an efficient time-based coordinated checkpointing protocol for mobile computing systems is proposed. The main difference from traditional time-based protocols is that our protocol tries to reduce the number of checkpoints per checkpointing process, at the expense of only a small number of coordinating messages. Additionally, the protocol improves the mechanism of timer synchronization by taking advantage of the reliable timers in the mobile support stations, so that it is well adapted to mobile computing systems over wide area networks.