This paper addresses the performance analysis for orthogonal space-time block coded (STBC) multiband orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) systems. As the channel model considers the log-normal fading, the resultant signal to noise ratio (SNR) will be the product of a log-normal distributed variable and a variable of sum of several Gamma- distributed variants. Based on this, the exact expressions for the bit error probability and the outage probability are derived theoretically. And their approximate expressions can be obtained via the Gauss-Hermite and the Gauss- Laguerre quadratures, respectively. Simulation results verify the theoretical solutions.