Monodisperse amorphous-selenium spherical colloids (see Figure) have been synthesized in large quantities by reducing selenious acid with hydrazine in ethylene glycol. The diameters of these colloids could be controlled in the range of 90-420 nm by adjusting the molar ratio between selenious acid and hydrazine. The as-obtained colloids could be readily crystallized into long-range-ordered three-dimensional lattices with well-defined Bragg-diffraction peaks.