In this paper, the performance of a secondary user (SU) in an underlay cognitive radio (CR) network over a generalized-gamma (GG) fading channel in terms of three performance metrics, namely, outage probability, ergodic capacity, and bit error rate (BHR), is investigated. According to the url, tor lay approach, the transmit power of the SU should limited to avoid interference to primary users (PUs). The performance metrics of the SU In the underlay CR network are theoretically derived and also obtained with Monte Carlo simulations for a GG fading channel with different fading paramet: To demonstrate the effect of limited power on the performance metrics, three different maximum transmit power levels (P-max), namely, 10, 20, and 30 dB, are used. The simulation results lead to three conclusions: First, when high values are chosen for the fading parameters (alpha, c), the fading channel gets less distorted and the performance metrics Improve. The second conclusion is that the BER performance gets better as the limited power increases. The final conclusion is that the BER performance of SUs Improves as the interference power that SUs can tolerate increases..