This paper introduces Quaternion Encryption Scheme (QES) as a means to secure signal transmission over wireless networks that are vulnerable to attacks. Sampling data of the signal are formulated in a 3-D vector space and are rotated by another key vector space parameter using quaternion representation. Quaternion is used to generate four-dimensional encryption keys, which significantly eliminates the risk of eavesdropping. Furthermore, quaternion has capability to provide a meditative encryption system for wireless images or voice transmissions. A computer-based simulation conducted to scrutinize carefully the capability of QES in insuring the highest level of security is reported.