Single-crystalline rhombic Ag 2 S hollow nanoparticles with uniform size and shape were synthesized by a simple solution-phase method at 45°C. The obtained products were determined by X-ray powder diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The possible mechanism was discussed for the formation of rhombic hollow nanoparticles. The rhombic hollow nanoparticles could self-assemble into ordered arrays through “bottom-up” assembly. The ordering over a distance was up to several micrometers and even larger, which might hold technological promise for nanomaterial and nanodevice fabrications in the future.