Perhydrolysis of various tris(alkoxy)boranes B(OR)3 with R = CH3, n-C3H7, tert-C4H9 or n-C8H17 in the presence of lithium alkoxides LiOR′ where R′ = CH3, C2H5, n-C4H9 or tert-C4H9, or in the presence of RbO-n-C4H9, tert-butylamine or cyclohexylamine in alcoholic media other than methyl alcohol yields with H2O2/H2O (85:15 by weight) the peroxoborates LiBO3,7 · H2O, RbBO4 · 0,5 H2O, tert-C4H9NH3BO4 · 0,5 H2O or cyclo- C6H11NH3BO4 · H2O, with H2O2/H2O (98:2 by weight) LiBO3,8 - H2O, RbBO4,7 · H2O, tert-C4H9NH3BO5 · H2O or cyclo-C6H11NH3BO4,8 · H2O.H2O2/H2O (98:2 by weight) was prepared by a modified method.With reference to stabilities, IR spectra and NMR spectra, the structures of these noncrystalline polyborates are discussed. All the compounds contain the active oxygen in the form of B-O-O-groups