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　O-2-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.　(C)　2019　Hydrogen　Energy　Publications　LLC.　Published　by　Elsevier　Ltd.　All　rights　reserved.