Using X-ray diffraction and differential scanning calorimetry (DSC) the structure and the crystallization mechanism of Se0.8Te0.2 chalcogenide glass have been studied. From the radial distribution function, the short-range order of the amorphous phase has been discussed. The lattice parameter of the crystalline phase has been determined by using the Cohen least-squares method. The results of the thermal analysis indicate that the crystallization process is a two- dimensional growth. The calculated value of the effective activation energy for crystal growth, EG, is 160.8 ± 0.1 kJ/mol. The calculated lattice parameters a and c of the hexagonal crystalline phase are 0.4398 ± 0.0014 and 0.5055 ± 0.0021nm, respectively.