Carrier sensing mechanism has been adopted in IEEE 802.11 MAC for collision avoidance under single channel based wireless ad hoc networks. However, due to the hardware limitation, the carrier sensing mechanism can not help much in single transceiver and multi-channel scenarios. In this paper, we propose a pipelining multi-channel (pi-Mc) MAC protocol for multi-channel ad hoc networks. The core idea of pi-Mc is similar to the pipeline technique. Without collecting each channel usage information, pi-Mc not only uses overall channel resources for transmission, but also can prevent DATA collisions. The performance of pi-Mc is compared with two well-known multi-channel MAC protocols and IEEE 802.11 DCF. Simulation results show that pi-Mc is able to achieve 2.50 times the throughput of IEEE 802.11 DCF, as well as respectively outperform DCA and MMAC with a factor of up to 1.43 and 1.32 under three available channels.