The isothermal crystallization kinetics of pure fused quartz of blank specimen N-0 and specimen N-3 introducing 3 mass% nano-Nd₂O₃ were researched by means of XRD and Avrami equation. The results show that crystallization mechanisms of fused quartz in two specimens are both heterogeneous nucleation type caused by surface structure defects, and the grain growth modes of two specimens are both two-dimensional growth accompanied by one-dimensional and three-dimensional growths, specimen N-3 has the higher degree of grain growth in one-dimensional and three-dimensional than specimen N-0; introducing nano-Nd₂O₃ can obviously reduce the “active nucleation sites” of glass structure on the fused silica particles surface, enhance the stability of glass structure, increase the activation energy of fused quartz crystallization from 874 kJ·mol^-1 to 1 270 kJ·mol^-1, and decrease the crystallization rate of fused quartz obviously.