In mobile ad hoc networks (MANET), deploying a small number of mobile relays can greatly improve the throughput, delay, and security performance. However, in such a hybrid MANET, it is challenging to determine the optimal locations of mobile relays. In this paper, we study a mobile relay placement problem to maximize the network throughput of hybrid MANET with secure network coding capability. Specifically, we first study the maximal throughput of a hybrid MANET, in which the position of each mobile relay is known. For such a special case, we model the maximal throughput problem as a linear programming problem. On the basis of the understanding of this problem, we then formulate the optimal relay placement problem as an integer linear programming problem. Because integer linear programming is too complex to solve for a large MANET, we propose an efficient near-optimal approximation algorithm based on linear programming-relaxation. Finally, we conduct extensive simulation experiments, which demonstrate the effectiveness of the proposed algorithms. Copyright © 2013 John Wiley & Sons, Ltd.