The demand for the frequency spectrum is increased everyday which is a natural and limited source. With many new wireless services provided, wireless communication systems grow rapidly, and increasing the demand for spectrum. Cognitive Radio (CR) is proposed as a revolutionary solution to the conflict between increasing spectrum demand and finite spectrum resources. Spectrum sensing is an essential component used in CR to effectively improve the utilization of the spectrum. In this study, an algorithm for energy based spectrum sensing by using wavelet transform approach is presented and simulation results are given.