Nanocrystallized glasses with the composition of 40BaO•20TiO₂•40SiO₂, stoichiometric to fresnoite (Ba₂TiSi₂O₈), have been prepared by heat-treatment at various temperatures, and their optical properties, second-harmonic generation (SHG) and photoluminescence (PL), have been examined. The glass subjected to the heat-treatment at 760°C for 1 h showed a dense formation of Ba₂TiSi₂O₈ crystals with the dimension of 200-300 nm, and maintained a visual transparency. Visible green light corresponding to SHG at 532 nm was confirmed in the transparent Ba₂TiSi₂O₈ nanocrystallized glasses. The maximum second-harmonic intensity in the nanocrystallized samples was on the order of 1/100 when compared to that of an α-quartz single crystal. Furthermore, the bluish white PL with a peak at the wavelength of about 470 nm was also visually observed in samples heat-treated at 750-800°C.