Mechanical activation-triggered crystallization in PbNb2O6-based glass was dependent on the initial presence of nuclei. The crystallization cannot be initiated by mechanical activation in a highly amorphous glass composition quenched from 1350 degreesC where PbNb2O6 nuclei did not exist. The steady growth of nanocrystallites of PbNb2O6 was observed with an increasing degree of mechanical activation in the glass quenched from 1300 degreesC, where a density of PbNb2O6 nuclei existed before mechanical activation. The inability to nucleate in the highly amorphous oxide glass by mechanical activation is consistent with the much higher structural stability as compared with that of metallic glasses, such as Fe-Si-B. The mechanical activation-grown PbNb2O6 nanocrystals were 10-15 nm in size as observed using HRTEM and their crystallinities were further improved by thermal aging at an elevated temperature in the range of 550 degrees to 650 degreesC.