Single crystals of magnesium tin oxyborate, Mg 5 SnB 2 O 10 (Mg 5 SnO 4 (BO 3 ) 2 ), were prepared at 1350°C in air, using B 2 O 3 as a flux. They were colorless and transparent with needlelike or columnar shapes. X-ray diffraction analysis of the single crystals revealed that Mg 5 SnB 2 O 10 crystallizes in the triclinic space group F1 (No. 2) with Z = 16, a = 6.1295 (8), b = 18.714(3), c = 24.719(3) Å , R = 90.021(5)°, β = 90.032(4)°, γ = 90.041(5)°, and V = 2835.4(7) Å 3 (R1 = 0.0168, wR2 = 0.0459, and S = 1.297 for all data). The crystal structure of Mg 5 SnB 2 O 10 is a ludwigite-type superstructure. Mg and Sn atoms are ordered and coordinated by six O atoms, and the edges of MO 6 (where M = Mg and Sn) octahedra are connected along the a-axis and form zigzag walls. B atoms are in the spaces surrounded by the walls and are coordinated by three O atoms. Polycrystals of titanium(IV)-doped solid solutions, Mg 5 Sn 1-x Ti x B 2 O 10 (0 < x e 0.50), were also prepared by solid state reaction at 1300°C in air. The refined unit cell volumes decreased with increasing titanium content (x), indicating partial substitution of Ti for Sn atoms. A broad blue emission with a peak wavelength of ∼430 nm was observed from the solid solutions under 265-nm ultraviolet excitation. A quantum efficiency of 0.81 was measured at room temperature for Mg 5 Sn 0.80 Ti 0.20 B 2 O 10 .