A computational method independent of experimental protein structure information is proposed to recognize key residues in protein folding, from the Study of hydration water dynamics. Based on all-atom molecular dynamics simulation, two key residues are recognized with distinct water dynamical behavior in a folding process of the Trp-cage protein. The identified key residues are shown to play an essential role in both 3D structure and hydrophobic-induced collapse. With observations on hydration water dynamics around key residues, a dynamical pathway of folding can be interpreted. (C) 2010 Elsevier Inc. All rights reserved.