Clock synchronization is a critical service for many network applications. In mobile ad hoc networks, traditional clock synchronization algorithms like NTP are not applicable due to the mobility of nodes. Reference broadcast synchronization (RBS) takes advantage of the broadcast communication property in wireless networks and can achieve high accuracy in one broadcast domain, but RBS is not scalable to mobile and multiple hop situations. In this paper, we propose a new clock synchronization algorithm for multihop mobile ad hoc networks. Our approach utilizes RBS in one broadcast domain and uses an approximate Minimum Connected Dominating Set (MCDS) to extend RBS based synchronization to multiple hops. Simulations show that our algorithm achieves very high accuracy in synchronization and adaptive to the mobility of the network nodes.