Polymeric　self-solidifying　ionic　liquids　(PSILs)　were　simply　fabricated　by　the　facile　nucleophilic　substitution　reaction　between　polyethyleneimine　(PEI)　and　1,3-propanesultone　(PS).　Because　of　the　presence　of　less-substituted　amino　groups　in　PEI　chain,　more　than　1　equivalents　of　sulfonic　groups　(–SO3H)　per　amino　group　were　grafted　onto　PEI　chain.　Part　of　–SO3H　groups　could　be　bonded　with　amino　groups　to　form　–SO3–…N+–　zwitterions,　the　presence　of　zwitterion　and　the　high　molecular　of　PEI　could　make　PSILs　become　solid,　while　the　left　free　–SO3H　groups　played　a　role　in　the　acid　catalysis　and　therefore　no　additional　acids　were　required.　The　final　PSILs　showed　high　catalytic　activity,　stability　and　generality　as　the　heterogeneous　catalysts　for　biodiesel　production　via　the　esterification　of　a　variety　of　free　fatty　acids　(FFAs),　as　well　as　the　transesterification　of　waste　cooking　oil　and　palm　oil.　Moreover,　the　one-step　fabrication　process　of　PSILs　is　much　simpler　than　the　multi-step　fabrication　process　of　traditional　ionic　liquids,　suggesting　potential　benefits.　©　2021