A new perovskite-like oxide (Rb₂Nd₂Ti₃O₁₀) is synthesized by the ceramic method. Its stability in a humid atmosphere and aqueous solutions of different acidities is investigated. Under these conditions, the formation of hydrated and protonated compounds is revealed. The parameters of the unit cell of the Rb₂Nd₂Ti₃O₁₀ oxide and its derivatives and the degree of rubidium substitution by protons for the obtained protonated phases are determined.