To functionalize Au MPCs (monolayer-protected gold clusters), ligand place-exchange reactions provide a convenient route in which the initial capping ligands are displaced by mixing the MPCs with an excess amount of incoming ones. However, literature reports show that the diameters of the modified products do not always stay unchanged. Because of the diversity of experimental conditions carried out in the documented studies, there is still a lack of comprehensive understanding concerning the size evolution. Herein, carefully controlled and examined parameters include the initial size of MPCs [Au-101(PPh3)(21)Cl-5], the reaction time, the concentration of incoming ligands, a homologous series of incoming ligands, and the anchoring headgroups. The results show that the final particle size is determined by the strength of headgroup gold adsorption which is correlated with the curvature of the final product in a thermodynamic model derived from Gibbs Thomson equation.