Zn2−xMnxSiO4 phosphors were synthesized by a hydrothermal process using ZnO and SiO2. Prismatic Zn4Si2O7(OH)2 · H2O particles were formed through heterogeneous nucleation on the surface of the ZnO particles. The Zn2SiO4 phase was formed through an isometric phase transition of Zn4Si2O7(OH)2 · H2O. Water pressure, as well as the particle size of the raw materials, had a profound effect on the temperature of phase formation. The effect of solution pH on the morphology and growth of the particles was investigated. The photoluminescence of the synthesized Zn2−xMnxSiO4 phosphor was also examined. The color coordinate of the Zn2−xMnxSiO4 phosphor obtained in this study showed a green color, which was shifted toward short wavelength.