The results of X-ray structural analysis, in situ powder high temperature X-ray diffraction (HTXRD), DTA and annealing studies are summarized to refine the phase equilibria in the Rb₂O-B₂O₃ system in air. Samples were prepared by solid state reaction as well as by the crystallisation of glasses. Investigations show that, in the latter case, high-temperature metastable phases crystallise first, and it takes some months to reach phase equilibria. The recent determination of crystal structures of Rb₂B₄O₇, Rb₃B₇O ₁₂, Rb₃B₁₉O₃₁, α,β- RbB₃O₅ and β-RbB₅O₈ along with the HTXRD and DTA study led to substantial revising of the Rb ₂O-B₂O₃ phase diagram between the 5-50 mol. % Rb₂O compositions. New compounds Rb₂B₇O ₁₂ and Rb₅B₁₉O₃₁ and new phase relations in this connection are presented. The low (α) and high temperature (β) modifications of RbB₃O₅ were discovered and α↔β transition is studied in details by powder HTXRD.