Extensive structural studies using high-pressure NMR spectroscopy have recently been carried out on proteins, which potentially contribute to our understanding of the mechanisms of protein folding. Pressure shifts the conformational equilibrium from higher to lower volume conformers. If the pressure is varied, starting from the folded native structure, in many cases we observe intermediate conformers before the onset of total unfolding. This enables the investigation of details of the structure and thermodynamic characteristics of various intermediate conformers of proteins under equilibrium conditions. We can also examine pressure effects on the structure and stability of some typical denatured states such as helical denatured, molten globule, and unfolded states. The high-pressure NMR method can also be used to investigate association/dissociation equilibria of oligomeric or aggregated proteins. Beside direct observation of kinetic intermediates upon pressure jump, NMR structural investigations of equilibrium conformers under pressure provide information about the structures of kinetic intermediates during folding/unfolding reactions.