This paper presents a performance evaluation in terms of bit error rate (BER) of a 26 GHz-band ultra-wideband (UWB) communication system through measurement-based simulation. We measured real channel responses in an office to obtain responses for use in simulations. The simulation results demonstrate that the 26-GHz-band UWB system can achieve high-speed data transmission of 500 Mbps or more, in and indoor office by using a directional antenna.