Wireless sensor networks consist of a network of autonomous sensors that can reconfigure themselves so as to sense the environment in the most significant manner. However, a significant challenge in the practical application of these networks exists in credible authentication and network security. This paper proposes a secure authentication protocol which is considered as a pro-active method, where a user is strongly verified before accessing the data, it is the modified Adhoc On-Demand Distance vector (AODV) Routing protocol that provides many security principles to the user such as checking sequence number, IP address and threshold values. The performance of proposed algorithm is compared with the existing alogorithm based on the following parameters such as Throughput, End to End delay and packet delivery ratio. The results shows that the proposed protocol possesses many advantages against the popular black hole attack. This work has been carried out using NS2 software and the result obtained testifies the effectiveness of the proposed protocol. Keyword: Authentication protocol, AES security, AODV routing protocol, Black hole attack, Wireless sensor network (WSN).