Sr2ZnTeO6 double-perovskite oxide has been synthesized using solid state chemistry. As synthesized, the crystalline structure of Sr2ZnTeO6, refined using x-ray diffraction, is monoclinic having the space group I2/m. Structural phase transitions are studied using Raman spectroscopy in the temperature range 25 degrees C-567 degrees C. It is found that two of three observed bending Raman vibrations merge together at a temperature of around 120 degrees C, indicating a Sr2ZnTeO6 phase transition from the monoclinic (I2/m) to the tetragonal (I4/m). Furthermore, a temperature-dependence change-rate of external and O-Te-O bending modes and stretching modes are detected at 270 degrees C, which is interpreted as a phase transition from the tetragonal (I4/m) to the cubic (Fm-3m) structure.