In this paper, we present a Secure Routing Protocol for Sensor Networks (SecRout) to safeguard sensor networks under different types of attacks. The SecRout protocol uses the symmetric cryptography to secure messages, and uses a small cache in sensor nodes to record the partial routing path (previous and next nodes) to the destination. It guarantees that the destination will be able to identify and discard the tampered messages and ensure that the messages received are not tampered. Comparing the performance with non-secure routing protocol AODV [1] (Ad hoc on Demand Distance Vector Routing), the SecRout protocol only has a small byte overhead (less than 6%), but packet delivery ratio is almost same as AODV and packet latency is better than AODV after the route discovery.