Biodiesel　produced　from　non-edible　oils　has　received　intensive　attention　in　recent　years.　Herein,　a　series　of　novel　amphipathic　ionic　liquids　(ILs)　based　on　the　4-dimethylaminopyridine　(DMAP)　were　prepared　for　the　transesterification　of　soapberry　oil　and　methanol.　The　structures　of　the　prepared　ILs　were　systematically　characterized　by　both　Fourier　transform　infrared　spectroscopy　(FT-IR)　and　nuclear　magnetic　resonance　(NMR,　1H　NMR　and　13C　NMR).　In　addition,　the　effects　of　side-chain　length　of　cation　and　the　number　of　active　site　(H+)　of　ILs　on　the　biodiesel　yield　were　investigated,　and　the　results　suggested　that　1-dodecyl-(4-dimethylammonium)-pyridinium　bisulfate　([C12-DMAPH][HSO4]2)　exhibited　the　highest　catalytic　efficiency.　Meanwhile,　[C12-DMAPH][HSO4]2　was　proven　to　be　amphipathic,　and　the　corresponding　catalytic　mechanism　was　proposed.　Under　the　catalysis　of　[C12-DMAPH][HSO4]2,　the　optimum　operating　conditions　of　transesterification　of　soapberry　oil　and　methanol　were　explored　via　the　combination　of　single　factor　experiment　and　response　surface　methodology,　obtaining　the　high　biodiesel　yield　of　(98.02　±　0.36)%　under　the　optimum　operating　conditions.　Importantly,　[C12-DMAPH][HSO4]2　exhibited　high　stability　in　the　transesterification　of　soapberry　oil　and　methanol　in　five　consecutive　runs.　Furthermore,　the　catalytic　activities　of　[C12-DMAPH][HSO4]2　towards　other　transesterification　of　non-edible　oils　and　lower　alcohols　were　also　investigated,　which　indicated　a　general　applicability　of　the　prepared　IL.　©　2020　Elsevier　Ltd