In the presence of both transmitter (TX) and receiver (RX) IQ imbalances, the TX/RX IQ imbalances and channel fading are coupled together. Therefore, one needs to solve a set of highly nonlinear equations for estimating the TX/RX IQ imbalance parameters and channel transfer functions at subcarriers in OFDM systems. In this paper, a novel joint TX/RX IQ imbalance estimation and compensation scheme is proposed. By taking advantage of the frequency-selective channel fading, the TX/RX IQ imbalance parameters and channel transfer functions can be decoupled and estimated sequentially. Simulation results demonstrate that the proposed scheme can effectively estimate and compensate the TX/RX IQ imbalances in OFDM systems.