Mobile Ad hoc Networks (MANET) are wireless networks without an infrastructure, which are usually set up on a temporary basis to serve a particular purpose within a specific period of time. The importance of MANET can never be over-emphasized as it has found applications in so many fields of human endeavor. An efficient routing protocol for MANET has become a necessary and important issue to be considered before deploying any mobile network. In our thesis, we investigated the effects of cache size and cache expiry time on the overall performance of the Dynamic Source Routing protocol which is basically on-demand. Detailed simulations were carried out, using OPNET Modeler 14.5, on 20 and 30 mobile nodes networks for different values of path cache size and cache expiry time. One can intuitively assume that the larger a path cache size and the cache expiry time, the better the performance of the routing protocol. Nevertheless, as can be shown in our simulation results, a smaller cache capacity can indirectly affect the performance of the routing protocol and the cache expiry time has an infinitesimal or no effect on the performance of the dynamic source routing protocol for MANET. Keywords: MANET, DSR, Route Cache, Cache Size, Cache Expiry time, Routing Protocols.