Introduction: Understanding the binding mechanism between gold nanoparticles and biomolecules is a fundamental step for numerous applications in biosensors and targeted drug delivery. This study aims to clarify the adsorption behaviors of CYS and GSH on the gold surface using a small gold Au8 cluster as a model reactant. Methods: Here, we examine in details the molecular interaction between Au8 cluster with cysteine (CYS) and glutathione (GSH) by means of density functional theory (DFT). The PBE functional is employed in combination with the cc-pVTZ basis set for non-metal atoms and the cc-pVTZ-PP basis set for gold. Harmonic vibrational frequencies are also computed to confirm optimized geometries as local minima or transition states on the potential energy surfaces. Results: The calculated results show that these molecules prefer to anchor on the gold cluster via the sulfur atom with the adsorption energies of 20.3 and 30.8 kcal/mol for CYS and GSH, respectively, in gas phase. In water, such values are considerably reduced, namely 19.0 kcal/mol for CYS and 26.4 kcal/mol for GSH. If a visible light with a frequency of n = 6x10^14 Hz (500 nm) is applied, the time for the recovery of CYS and GSH from the most stable complexes will be about 1.24 and 6.03x10^7 seconds at 298 K in gas phase. Conclusion: The Au8 cluster could be a promising material for designing sensor in CYS and GSH selective detection.