This work aims to analyze the performance of Orthogonal Frequency Division Multiplexing (OFDM) applied in the fourth generation mobile networks and WiFi. Fuzzy logic technique is used in this study to analyze the problem of OFDM, taking into consideration the modulation techniques applied in OFDM. Three input parameters in the fuzzy logic system are mainly considered: signal-to-noise ratio, the modulation degree and the number of sub-carriers. The output parameters are selected to be the bandwidth and bit error rate. This requires an analytical study to determine the optimal values of the input parameters used in this study. This means studying the membership of functions of each input and output parameter using fuzzy logic.