Catalytic　methane　decomposition　is　a　promising　way　to　convert　methane　into　COx-free　hydrogen　and　value-added　carbon　nanomaterials,　but　the　development　of　a　sintering-resistant　catalyst　is　a　challenge.　In　this　study,　Ni–Ga/Al2O3　alloy　catalysts　with　different　Ga/Ni　atomic　ratios　were　prepared　from　Ni3−xGaxAl　(x　=　0–1.2)　hydrotalcite-like　compounds　(HTlcs)　as　precursors　and　tested　for　methane　decomposition.　Structural　and　physicochemical　properties　of　the　as-prepared　and　used　catalysts　were　characterized　by　ICP,　N2　physical　adsorption,　XRD,　H2-TPR,　H2　chemisorption,　STEM-EDX,　SEM,　TEM,　and　Raman　techniques.　The　results　indicate　that　upon　calcination　at　500　°C,　Ni–Ga–Al　HTlcs　are　transferred　to　rock-salt　Ni(Ga,Al)O　oxide　solid　solutions,　and　reduction　with　H2　at　800　°C　leads　to　single-phase　and　composition-uniform　Ni–Ga　alloy　particles　with　an　average　crystal　size　of　8–10　nm.　In　catalytic　methane　decomposition　at　600　°C,　the　alloying　Ni　with　a　suitable　amount　of　Ga　effectively　enhances　the　catalyst　life　and　carbon　yield.　Especially,　Ni2.4Ga0.6Al　shows　the　highest　carbon　yield　of　61.1　g-C/g-cat,　approximately　4.4　times　that　of　the　Ga-free　Ni　counterpart.　Meanwhile,　Ni–Ga　alloying　has　a　marked　influence　on　the　CNTs　geometry,　giving　herringbone-like　CNTs　with　small　diameters　and　thin　walls.　It　is　gratifying　to　find　that　the　Ni–Ga/Al2O3　catalyst　exhibits　good　resistance　against　sintering　under　the　adopted　reaction　condition,　which　accounts　for　the　formation　of　uniform　CNTs　of　smaller　size.　The　findings　provide　guidelines　for　the　control　of　carbon　morphology　and　geometric　size　in　methane　decomposition.　©　2022　Hydrogen　Energy　Publications　LLC