Biodiesel　is　an　attractive　alternative　to　fossil　fuels　due　to　the　energy　and　environmental　concerns.　In　this　paper,　seven　different　multi　–SO3H　functionalized　ILs　based　on　the　low-cost　less-substituted　amines,　which　contained　massive　sites　for　functionalization　of　sulfonic　acid　groups　and　further　treatment　of　sulfonate-based　anions,　were　prepared　as　catalysts　with　high　acidity　and　desirable　catalytic　activity　for　the　synthesis　of　biodiesel　from　the　esterification　of　oleic　acid　with　methanol.　The　physicochemical　properties　of　these　acidic　ILs　were　characterized　by　a　variety　of　analytical　techniques　such　as　FT-IR,　EA,　TGA,　and　the　Brønsted　acidity　was　well　determined　by　UV–vis.　Among　the　ILs　prepared,　[EDA-PS][P-TSA]　showed　the　highest　catalytic　activity　for　esterification　due　to　its　high　acidity　and　appropriate　miscibility　with　reactants,　with　an　ultrahigh　97.58%　conversion　of　oleic　acid　under　the　optimum　conditions　(i.e.　reaction　time,　1.8　h;　catalyst　amount,　3　wt%;　alcohol/acid　molar　ratio,　13:1,　temperature　70　°C)　acquired　from　the　Box–Behnken　response　surface　methodology.　With　the　novel　strategy　of　multi　–SO3H　modification　on　ILs,　our　catalyst　had　an　approaching　or　even　superior　oleic　acid　conversion　rate　compared　to　other　reported　catalysts　with　considerably　lower　catalyst　dosage　and　shorter　reaction　time.　More　importantly,　it　also　exhibited　high　generality　for　converting　various　FFA　feedstocks　into　biodiesel　with　considerable　conversion　within　93.59–94.33%　under　a　rather　lower　catalyst　dosage,　which　showed　the　valuable　potential　for　converting　low-cost　oils　into　biodiesel　from　an　economic　and　environmental　perspective.　©　2020　Institute　of　Process　Engineering,　Chinese　Academy　of　Sciences