The crystal structure of Rb₂B₄O₇ is described, the first structure determined for anhydrous rubidium borates. It belongs to the triclinic system, sp. gr. P1; a = 9.860(4), b = 10.653(6), c = 6.649(4) Å; α = 103.4(1), β = 101.4(1), γ = 89.1(1)°; V = 665.5 ų; Z = 4; d_calc = 3.26 g/cm³. The atomic coordinates of atoms of the isostructural K₂B₄O₇ compound were used in the anisothropic approximation, R=0.053. The structure consists of a three-dimensional skeleton formed by three kinds of mixed anions: [B^IIIO_1.5]⁰ triangles; [B^IV₂ B^IIIO_5.5]^2- simple rings consisting of two tetrahedra and a triangle; and [B^IV₂ B^III₂ O₇]^2- double rings formed by [B^IV₂ B^IIIO_5.5]^2- simple rings of two shared tetrahedra.