Wireless Sensor Networks finds its applications in various domains like agriculture, tracking, controlling, surveillance tasks, military, structure monitoring etc. as they can be operated in unattended hostile & public environments. This paper enlightens on various biometric security system providing authentication for the legitimate users in Wireless Sensor Networks. Wireless Sensor Networks security requires confidentiality, authentication & integrity. Biometric authentication is known for its knowledge-based & possession-based techniques which encourages a secure communication. A brief overview of sensor networks and security issues, biometric system and authentication systems are discussed.