Ammonia　decomposition　is　a　promising　method　for　on-site　hydrogen　generation　for　fuel　cells.　Ruthenium　is　the　most　active　catalyst　for　this　process,　and　modulation　of　its　geometric　and　electronic　properties　is　essential　for　achieving　high　catalytic　performance.　This　study　developed　a　facile　approach　for　synthesizing　alkali　metal-doped　Ru/MgO　catalysts　using　a　one-pot　dry　ball　milling　method　with　acetates　as　precursors.　Characterization　results　indicate　that　K,　Rb,　and　Cs　act　as　effective　structural　and　electronic　promoters.　Notably,　the　presence　of　alkali　metals　significantly　inhibits　the　aggregation　of　bulk-like　RuO2,　leading　to　the　formation　of　well-dispersed　RuOx,　which,　upon　reduction,　produces　small　Ru　nanoparticles.　The　average　Ru　particle　size　is　about　2-3　nm,　aligning　with　the　theoretical　optimal　size　for　maximizing　B5　sites.　XAS　and　DRIFTS　analyses　confirm　that　Ru　species　are　stabilized　due　to　the　strong　metal-promoter　interaction　between　ruthenium　and　alkali　metals　via　oxygen　bonding.　The　resulting　alkali　metal-promoted　Ru　nanoparticles　exhibit　superior　low-temperature　activity　for　ammonia　decomposition.　The　2　K-3　%Ru/MgO　catalyst　achieves　a　high　reaction　rate　of　11.5　mmol-NH3　gcat-1　min-1　at　400　degrees　C　under　30,000　mL　gcat-1　h-1,　demonstrating　one　of　the　highest　performances　among　Ru　catalysts.　Furthermore,　this　catalyst　maintains　high　activity　at　475　degrees　C　for　50　h　without　significant　deactivation.　The　enhanced　catalytic　performance　is　attributed　to　the　structural　and　electronic　promotion　effects　of　alkali　metals,　which　facilitate　the　formation　of　B5　site-rich　and　electron-rich　Ru　nanoparticles.　These　findings　offer　valuable　insights　into　the　role　of　alkali　metals　and　provide　helpful　guidance　for　designing　efficient　alkali　metal-promoted　ruthenium　catalysts　for　practical　applications.