A key problem in network coding (NC) lies in the complexity and energy consumption associated with the packet decoding processes, which hinder its application in mobile ad hoc networks (MANETs). Sliding-window Network Coding is a variation of NC that is an addition to TCP/IP and improves the throughput of TCP on MANETs. In this paper, we propose an Adaptive Length Sliding Window-based Network Coding for Energy Efficient algorithm in MANETs (ALSW-NCEE). The performance of this ALSW-NCEE is studied using NS2 and evaluated in terms of the network throughput, encoding overhead, energy consumption, and energy efficiency when packet is transmitted. The simulations result shows that the ALSW-NCEE with our proposition can significantly improve the network throughput and achieves higher diversity order.