The crystallization behavior of zinctellirite (20ZnO·80TeO₂) glass at different rates of heating and cooling were studied by an in situ high-temperature X-ray diffractometer (a rapid measurement system). During the heating process, α-TeO₂ and ZnTeO₃ were found to crystallize first, followed by the crystallization of Zn₂Te₃O₈. While during the cooling process from melt, α-TeO₂ was found to crystallize first, followed by the crystallization of Zn₂Te₃O₈. The results of crystallization behavior of the 20ZnO·80TeO₂ glass were compared with a Temperature-Time-Transfer diagram of the corresponding glass reported by Todoroki et al.