Protein hydration water is responsible for the biological activity of the protein itself. This is true for all proteins that in fact become active with at least a hydration level h=0.2 (g of water/g of dry protein). For lysozyme at low temperature, below 220 K the strong rigidity of the low-density hydrogen bond network extended on the protein surface inhibits protein side-chains motion. At high temperature, above 346 K, the very short lifetime of hydrogen bonds lets the protein unfold irreversibly. Below this temperature a reversible folding/unfolding process exists, in which lysozyme folds and unfolds rapidly as a function of temperature and permanence time. In this work, we present a proton Nuclear Magnetic Resonance study at very high resolution of the kinetic equilibrium that characterizes the folding/unfolding process of hydrated lysozyme.