In-situ Raman spectroscopic measurements of lawsonite in the OH and H2O stretch-ing region were conducted up to approximately 2.5 GPa and 400 ℃ with a hydrothermal diamond-anvil cell. In the experimental design at room temperature, the ratio of band-area and the width at half maximum of the decomposed Raman band shows discontinuities at 0.8 GPa, and correspondingly, the 695-cm-1 peak in the low-wavenumber region was split into two peaks. In the experiments at high temperature, the splitting of the 695-cm-1 peak was induced at 2.4 GPa and 250 ℃. These findings demonstrate the existence of discontinuities in the pressure response of the strength of the hydrogen bonds, which suggests a possible change of the hydrogen-bonded structure in lawsonite under these conditions. In the experimental Raman spectroscopic measurements of lawsonite in the OH and H2O stretch-ing region were conducted at about 2.5 GPa and 400 ° C with a hydrothermal diamond-anvil cell. In the experimental design at room temperature, the ratio of band-area and the width at half maximum of the decomposed Raman band shows discontinuities at 0.8 GPa, and correspondingly, the 695-cm-1 peak was in the low-wavenumber region was split into two peaks. In the experiments at high temperature, the splitting of the 695 These findings demonstrate the existence of discontinuities in the pressure response of the strength of the hydrogen bonds, which suggests a possible change of the hydrogen-bonded structure in lawsonite under these conditions.