The influence of surface hydroxylation on nucleation and sintering of gold nanoparticles was studied by comparison of Au deposition and thermal sintering on ideally terminated MgO(001) and hydroxylated MgO thin films, respectively. A combination of different spectroscopic techniques (TDS, XPS, IRAS) allows to establish a correlation between the degree of surface hydroxylation and the stability of gold atoms and clusters. Hydroxyl groups destabilize gold atoms on the MgO surface at 90 K; however, they enhance the stability of small gold clusters toward sintering at higher temperature.