Silicon-germanium (SiGe) alloy nanocrystals (NCs) are promising for advanced optoelectronic applications due to their highly tunable composition and photophysical behaviors. The homogenous dispersion of Si and Ge atoms on the surfaces of SiGe NCs adds a degree of freedom for manipulating the surface chemistry of this type of alloy material. However, the difference in the reactivity between Si and Ge atoms brings additional difficulty in selecting appropriate surface ligands to passivate SiGe NCs. Here we report a mixed-ligand functionalization approach to passivate SiGe NCs effectively. Octadecene and oleylamine molecules serve as co-ligands to cap the surface Si and Ge atoms, respectively, yielding colloidally stable SiGe NCs with high solution dispersity and stable intrinsic near-infrared emission with a microsecond-scale lifetime decay. The resulting particles also show improved hole and electron mobilities of up to 1.1 × 10-6 cm2 V-1 s-1 and 6.3 × 10-6 cm2 V-1 s-1, 2.2 and 1.2 times improvement over the particles only passivated by octadecene ligands.