Hydrotalcite-derived　Ni/Mg(Al)O　is　promising　for　CH4–CO2　reforming.　However,　the　catalysts　reported　so　far　suffer　from　sever　coking　at　low　temperatures.　In　this　work,　we　demonstrate　that　a　significant　improvement　of　coke-resistance　of　Ni/Mg(Al)O　can　be　achieved　by　fine　tuning　the　Ni　particle　size　through　adjusting　the　reduction　condition　of　catalyst.　Ni　particles　having　average　size　within　4.0–7.1　nm　are　in　situ　generated　by　reducing　the　catalyst　at　a　selected　temperature　within　923–1073　K.　Controllability　of　Ni　particle　size　is　related　to　the　formation　of　Mg(Ni,Al)O　solid　solution　upon　hydrotalcite　decomposition.　It　is　found　that　the　catalyst　reduced　at　973　K　exhibits　high　activity,　stability,　and　coke-resistance　even　at　reaction　temperature　as　low　as　773　K.　In　contrast,　the　catalyst　reduced　at　923　K　has　low　activity　and　deactivates　due　to　Ni　oxidation,　while　those　reduced　at　1023　and　1073　K　suffer　from　sintering　and　severe　coking.　STEM　and　O2-TPO　reveal　that　coke　deposition　is　directly　proportional　to　the　Ni　particle　size　but　becomes　negligible　at　a　size　below　6.2　nm.　It　is　evidenced　that　a　critical　size　of　about　6　nm　is　required　to　inhibit　coking　effectively.　CO2　temperature-programmed　surface　reaction　indicates　that　the　deposited　carbon　on　small　Ni　particles　can　be　easily　removed　by　the　CO2　activated　at　the　Ni–Mg(Al)O　interfaces,　accounting　for　the　better　resistance　to　coking.　©　2019　Hydrogen　Energy　Publications　LLC