Wireless Sensor networks are a challenging task due to the lack of resources in the network as well as the frequent changes in network topology. Various routing protocols are designed basically to establish correct and efficient paths between source and destination. In the recent years, several routing protocols have been proposed in literature and many of them studied through extensive simulation at different network characteristics. In this paper, we compare the performance of three most common routing protocols of wireless sensor networks i.e. AODV, DSDV and ZRP. These protocols have been simulated using NS2 Package. This study investigates the routing protocols corresponding to packet delivery ratio, packet loss ratio, average throughput, dropped packets and end-to-end delay. Hence, evaluation and comparison between routing protocols is required because performance of any routing protocol can be changed with various parameters such as speed of nodes, pause times and number of nodes.