Metal nanoclusters have attracted extensive interests owing to their atomically precise structures as well as intriguing properties. However, silver nanoclusters are not as stable as their gold counterparts, impeding the practical applications of Ag nanoclusters. In this work, a strategy of free valence electron centralization was exploited to render parent Ag nanoclusters highly stable. The stability of Ag-29(SSR)(12)(PPh3)(4) (SSR: benzene-1,3-dithiol) was controllably enhanced by stepwisely alloying the Ag nanocluster to Ag17Cu12(SSR)(12)(PPh3)(4) and Au1Ag16Cu12(SSR)(12)(PPh3)(4). Specifically, the trimetallic Au1Ag16Cu12 is ultrastable even at 175 degrees C, which is close to the nanocluster decomposition temperature. The structures of Ag17Cu12 and Au1Ag16Cu12 nanoclusters are determined by single-crystal X-ray diffraction. Furthermore, a combination of X-ray photoelectron spectroscopy measurements and density functional theory calculations demonstrates that the enhanced stability is induced by the centralization of the free valence electrons to the interior of the nanocluster. More importantly, the Au1Ag16Cu12 enables the multicomponent A(3) coupling reaction at high temperatures, which remarkably shortens the catalytic reaction time from h to 3 min. Overall, this work presents a strategy for enhancing the thermal stability of nanoclusters via centralizing the free valence electrons to the nanocluster kernels.