Wireless sensor networks consist of some nodes that have limited processing capability, small memory and low energy source. These nodes are deployed randomly and often densely in the environment. In order to avoid malicious activities, the secure authentication scheme is required. Here, we have proposed the Secure Authentication based Multipath Routing Protocol (SAMRP) for improving network lifetime and providing data integrity in WSNs. It consists of three phases. In first phase, multipath route is integrated to ensure load balancing and avoid isolated failures. In second phase, encryption and decryption scheme is implemented to provide better authentication. Here three types of iterations are used during authentication phase. In third packet format is proposed for monitoring integrity and authentication status. So the efficient secure multipath route can be chosen to improve the network performance. By simulation results, the proposed SAMRP achieves better data delivery rate, improved network lifetime, high packet integrity rate, less end to end delay and overhead in terms of mobility, pause time, throughput, and number of nodes than the our previous scheme EMRTEM and existing scheme ADAPT.