This Mobile Ad hoc NETworks (MANETs) is a set of wireless mobile nodes dynamically form spontaneous network which works without centralized administration. Due to this characteristic, there are some challenges that protocol designers and network developers are faced with. These challenges include routing, service and frequently topology changes. Therefore, routing discovery and maintenance are critical issues in these networks. There are also limited battery power and low bandwidth available in each node. In this paper, the authors evaluate the performance of four MANET routing protocols using simulations: AODV, OLSR, DSR and GRP.