Crystallized glasses consisting of SrxBa1-xNb2O6 (SBN) nanocrystals (x=0.5, 0.61, and 0.62) with a tetragonal tungsten-bronze structure are synthesized using a conventional glass crystallization technique in xSrO-(32-x)BaO-32Nb(2)O(5)-36B(2)O(3) glasses with x=16, 19.5, and 24. Nanocrystals of Sr0.5Ba0.5Nb2O6, Sr0.61Ba0.39Nb2O6, and Sr0.62Ba0.38Nb2O6 are found to have rod-like shapes with an average diameter of 20-40 nm as determined from X-ray diffraction analyses and transmission electron microscope observations and to exhibit ferroelectricities as deduced from the presence of hysteresis in polarization-electric field curves. Although the optical transparency of crystallized glasses in the visible region decreases along with the formation of SBN nanocrystals, optical transparencies (sample thickness: similar to 1 mm, transmittance: similar to 80%) are observed at the wavelength of 1.55 mu m. Electrooptic activity was confirmed for the crystallized glasses with SBN nanocrystals, indicating that the present study would be a step for active optical device applications in glass-related materials consisting of SBN nanocrystals.