: This paper describes the implementation architecture and performance analysis of nanoMAC, a CSMA/CA based medium access control protocol, which is specifically designed for high density wireless sensor networks. We empirically show that nanoMAC performs with high reliability in a variety of network traffic conditions in single and multihop scenarios. For energy efficient operation and minimizing idleoverhearing, nanoMAC uses a specialized sleep algorithm. We also show results from a comparative study of nanoMAC with B-MAC in terms of performance measures, as well as their coexistence in networks deployed in overlapping or nearby areas.