Professor Gang Xiao was cited for his contributions to experimental condensed matter physics, in particular, in the giant magnetoresistance (GMR) and extraordinary Hall effect observed in magnetic granular solids, one of the most active research areas in condensed matter physics today. This novel effect promises a new generation of magnetic sensors and recording devices and also creates new opportunities for the understanding of the fundamental issue of spin-dependent electrical transport. Professor Xiao's group has uncovered many granular solids exhibiting GMR effects. He also found an important correlation between the Hall effect and GMR, making it necessary in theory to treat both GMR and the Hall effect on an equal footing. In a recent experiment he has clarified the mechanism of the GMR effect and characterized the effect of microstructure, temperature and magnetic field on the GMR effect. This work has generated strong interest in the GMR community and will provide important guidelines for achieving maximum GMR effect in granular solids.