Exploiting multiple channels improves the system performance in a heavy-loaded wireless ad hoc network. Many multi-channel MAC protocols have been proposed recently. The number of channels being used is fixed for these protocols, which limits their flexibility. As a result, these protocols may suffer from either longer delay in a light-loaded network or higher collision probability in a heavy-loaded one. In this paper, we propose a Load Awareness Multichannel MAC (LAMM) protocol which dynamically adjusts the number of channels being used according to the network load. Our scheme is able to utilize multiple channels to increase throughput when the network is heavily loaded. It can also switch back to use a single channel to reduce transmission delay when the network is lightly loaded. Simulation results verify that our LAMM significantly improves the network performance.