Aiming　to　address　the　mass　transfer　limitation　in　biphasic　transesterification　reactions　for　biodiesel　production,　as　well　as　the　poor　affinity　between　conventional　catalysts　and　feedstock　oils,　a　series　of　amphiphilic　heteropolyacid-based　sulfonic　acid-functionalised　ionic　liquids　(AHPA-SFILs)　were　synthesised.　Impressively,　the　solid-state　AHPA-SFILs　as　catalysts　would　dissolve　in　the　reaction　medium　during　the　transesterification　of　palm　oil　with　methanol,　enabling　efficient　homogeneous　catalysis.　Subsequently,　the　AHPA-SFILs　could　be　easily　precipitated　and　recovered　by　evaporating　the　methanol.　Under　the　reaction　temperature　of　140　°C,　methanol/oil　molar　ratio　of　20,　catalyst　dosage　of　7　wt%,　and　reaction　time　of　1.8　h　determined　by　response　surface　methodology,　the　optimum　AHPA-SFIL,　namely　[C16N-‍PS]-HPMo-1,　exhibited　a　95.86%　yield　of　biodiesel.　As　revealed　by　experiments　and　quantum　chemical　calculations,　the　C16　chain　of　[C16N-PS]-HPMo-1　on　one　hand　enhanced　the　mass　transfer　by　promoting　the　dissolution　of　methanol　in　oil　phase,　and　on　the　other　hand　facilitated　the　enrichment　of　triglycerides　through　intensified　van　der　Waals　interaction,　thereby　triggering　the　remarkable　catalytic　performance.　This　reaction　intensification　effect　derived　from　long　alkyl　groups　provided　a　theoretical　basis　for　the　design　of　future　ILs.　Furthermore,　[C16N-PS]-HPMo-‍1　AHPA-SFIL　showed　satisfactory　generality　in　the　biodiesel　production　from　different　oils,　signifying　its　promising　application　potential.　©　2023　Elsevier　Ltd