This paper presents a complete CMOS dual-conversion zero-IF2 transceiver for 9-band MB-OFDM UWB systems from 3.1 to 8.0 GHz. The transceiver integrates all building blocks including a variable-gain wideband LNA, a single mixer for both RF down and up conversions in RX and TX, a fast-settling frequency synthesizer, and IQ ADCs and DACs. Fabricated in a standard 0.18-μm CMOS process, the receiver measures maximum Sll of -13dB, maximum NF of 8.25 dB, in-band IIP3 of better than -13.7 dBm, and variable gain from 25.3 to 84.0 dB. IQ path gain and phase mismatch of the receiver chain are measured to be 0.8 dB and 4deg respectively. The transmitter achieves a minimum output P-1dB of -8.2 dBm, sideband rejection of better than -42.2 dBc, and LO leakage of smaller than -46.5 dBc.