Wireless Sensor Networks (WSN) suffers from variety of threats such as operational lifetime of sensor nodes and security for information carried by sensor nodes. There is an increasing threat of malicious nodes attack on WSN. Black Hole attack is one of the security threat in which the traffic is redirected to such a node that actually does not exist in network. Here we propose an approach to secure the multipath routing protocol in WSN by authentication process. The multipath routing protocol ensures the long life span of the wireless sensor network.