Guanidinium chloride is widely used to probe the folding/unfolding of protein and the denaturation mechanism of globular protein induced by guanidinium chloride is not fully understood.In this study, long time molecular dynamics simulations were carried out to investigate the denaturation of a 104-residue globular protein in aqueous guanidinium chloride.Though the complete unfolding of the protein was not observed in 500 ns simulations at 333 K, the secondary structures and hydrophobic core of the protein were perturbed.The guanidinium cations accumulated around the surface of the protein within 2 ns and prefered to interact with residues with negatively charged and planar side chains.Our study shows that guanidinium chloride caused the partial unfolding of the globular protein and the realistic molecular dynamics simulations can provide insight into the interaction modes between different kinds of residues and guanidinium cations at the atomic level, which can enhance our understanding about the denaturation mechanism of protein in guanidinium chloride solution.The study explored the denaturation of a globular protein in guanidinium chloride and the studied protein is one of the largest proteins used to probe denaturing mechanism, which provide more realistic picture of protein denaturation than the small model peptide.