The　x%Ni/Sm2O3-MnO　(x　=　0,　10,　15,　20)　catalysts　derived　from　SmMn2O5　mullite　were　prepared　by　solution　combustion　and　impregnation　method;　auto-thermal　reforming　(ATR)　of　acetic　acid　(HAc)　for　hydrogen　production　was　used　to　explore　the　metal-support　effect　induced　by　Ni　loadings　on　the　catalytic　reforming　activity　and　product　distribution.　The　15%Ni/Sm2O3-MnO　catalyst　exhibited　optimal　catalytic　performance,　which　can　be　due　to　the　appropriate　Ni　loading　inducing　a　strong　metal-support　interaction　to　form　a　stable　Ni/Sm2O3-MnO　active　center,　while　side　reactions,　such　as　methanation　and　ketonization,　were　well　suppressed.　According　to　characterizations,　Sm2O3-MnO　mixed　oxides　derived　from　SmMn2O5　mullite　were　formed　with　oxygen　vacancies;　nevertheless,　loading　of　Ni　metal　further　promoted　the　formation　of　oxygen　vacancies,　thus　enhancing　adsorption　and　activation　of　oxygen-containing　intermediate　species　and　resulting　in　higher　reactivity　with　HAc　conversion　near　100%　and　hydrogen　yield　at　2.62　mol-H-2/mol-HAc.