Pore　diffusion　effect　plays　a　crucial　role　in　heterogeneous　hydrogenation　of　unsaturated　polymers.　However,　how　large　pore　size　can　eliminate　the　pore　diffusion　limitation　remains　a　controversial　issue.　Herein,　we　prepared　a　series　of　Pd/SiO2　catalysts　with　graded　pore　sizes　and　investigated　the　effect　of　pore　size　on　hydrogenation　activity　of　nitrile　butadiene　rubber　(NBR).　It　is　found　that　when　the　catalyst　pore　size　(Dcat)　is　7　times　of　the　diameter　of　NBR　chains　(DNBR),　the　Weisz　modulus　0　can　be　reduced　to　＜　0.3　thus　the　internal　mass　transfer　limitation　can　be　eliminated,　making　NBR　easier　to　approach　the　active　sites.　Consequently,　the　catalysts　with　the　Dcat/DNBR　＞　7　exhibit　excellent　catalytic　activity　(96.7%)　and　selectivity　(100%)　to　C　=　C.　This　work　emphasizes　that　the　pore　size　of　catalysts　can　regulate　the　pore　transfer　limitation　and　the　accessibility　of　internal　active　sites,　providing　useful　guidance　for　the　design　of　efficient　macromolecular　hydrogenation　catalysts.　CO　2023　Elsevier　Ltd.　All　rights　reserved.