The ability to manipulate light over small length scales is the basis for many areas of technology, including communications, displays, and spectroscopy. Miniaturized mirrors, which are among the simplest waveguiding devices, are employed in spatial light modulators, in optical switches and as light emitting devices in commercial projection displays. Virtually all micromirrors are fabricated lithographically from metal-coated or uncoated silicon. We report here a scalable chemical synthesis of micrometer-scale mirrors based on Au nanoparticles and Ca2Nb3O10 nanoplates. Similar to their macroscale analogs, these nanoparticle mirrors (NMs) are capable of directional light reflection. Because of their small size, the NMs can be dispersed in polar and non-polar solvents, potentially allowing uses as optical probes to investigate the flow of liquids, or as fillers for polymers with tailored optical properties.