In general, Wireless Sensor Networks occur when sensor nodes are randomly left in an unreliable environment. Sensor node has limited processor, limited memory, limited radio capacity and low cost. In sensor network applications, security mechanisms must be used, because of unsafe environments, excessive number of sensor nodes, and wireless communication environments. Ensuring confidentiality, the primary goal of security, is one of the most important problems to be solved in order to realize time and vital objectives. While ensuring security, it is also necessary to consider other important criteria such as memory usage, energy and latency of Sensor Networks. In this study, encryption is described in Wireless Sensor Networks and Skipjack, XXTEA and AES encryption algorithms are compared using TOSSIM simulation program in TinyOS operating system considering memory usage, energy and delay criteria. The study is considered to be useful academicians who study security in Wireless Sensor Networks.