A new boroantimonate K_2SbB_3O_8 has been synthesized by high-temperature solidstate reactions, and its crystals have been obtained by the flux method. The crystal structure has been determined from single-crystal X-ray diffraction analysis. The compound crystallizes in the monoclinic space group P21/c with a = 5.8890(2), b = 11.0512(4), c = 10.8951(4) ?, β =103.200(4)°, V = 690.32(4) ?~3, Z = 4, F(000) = 672, ρc = 3.467 g/cm~3, Mr = 360.38 and μ = 5.215mm~(-1). Its structure feature is a three-dimensional framework composed of SbO_6 octahedra and isolated [B_3O_8]~(7-) groups with K+ cations residing in the one-dimensional tunnels along the a-axis.Interestingly, the isolated [B_3O_8]~(7-) groups are distinct from the known [B_3O_8]~(7-) groups, which always connect to each other. The UV-vis-NIR absorption, thermal stability and infrared spectrum are also discussed in this paper. A new boroantimonate K_2SbB_3O_8 has been synthesized by high-temperature solid state reactions, and its crystals have been obtained by the flux method. The crystal structure has been determined from single-crystal X-ray diffraction analysis. The compound crystallizes in the monoclinic space group P21 / c with a = 5.8890 (2), b = 11.0512 (4), c = 10.8951 (4), β = 103.200 (4) °, V = 690.32 (4) ) = 672, ρc = 3.467 g / cm ~ 3, Mr = 360.38 and μ = 5.215 mm -1. Its structure feature is a three-dimensional framework composed of SbO_6 octahedra and isolated [B_3O_8] groups with K + cations residing in the one-dimensional tunnels along the a-axis.Interestingly, the isolated [B_3O_8] ~ (7-) groups are distinct from the known [B_3O_8] ~ (7-) groups, which always connect to each other. The UV-vis-NIR absorption, thermal stability and infrared spectra are also discussed in this paper.