Nonideal sampling clocks in orthogonal frequency-division multiplexing (OFDM)-based ultra-wideband (UWB) systems introduce random timing jitter, which results in interchannel interference (ICI) and degrades the system performance. In this paper, we investigate the impact of timing jitter on OFDM-based UWB systems. We first derive an exact expression for the ICI power due to timing jitter. From the exact ICI power expression, we then develop various bounds on the ICI power under different situations. When timing jitters at different samples are independent, we obtain tight upper and lower bounds. When timing jitters at different samples are dependent, the ICI powers are different at different subcarriers and a universal upper bound for the ICI power is derived in this case. Compared with the exact expression for the ICI power, the developed bounds are easy to evaluate and provide insights. Their accuracy is confirmed by numerical examples. We also discuss the potential and the limitations of using oversampling to reduce the ICI power at the end.