This article is devoted to the investigation of water sorption by the layered perovskite-type titanate K₂Nd₂Ti₃O₁₀ and its intercalated protonated derivatives H_xK_2−xNd₂Ti₃O₁₀·yH₂O in a humid atmosphere. K₂Nd₂Ti₃O₁₀ was synthesized by the solid-state reaction. Metastable H_xK_2−xNd₂Ti₃O₁₀·yH₂O compounds were obtained by water flushing. The determination of the samples composition was carried out by XRD and TG analysis. The stability in a humid atmosphere was investigated by a water vapor sorption analyzer. It was found that humid atmosphere has influence only on K₂Nd₂Ti₃O₁₀ while H_xK_2−xNd₂Ti₃O₁₀·yH₂O phases are stable under experimental conditions. The study of K₂Nd₂Ti₃O₁₀ in humid atmosphere has shown that the intercalation process proceeds with a rate constant k_int = 3.2 × 10⁻⁶ min⁻¹ at 0–95% RH, and the protonation process takes place at RH more than 80%.