Flexible　conductive　materials　capable　of　simulating　transparent　ocean　organisms　have　garnered　interest　in　underwater　motion　monitoring　and　covert　communication　applications.　However,　the　creation　of　underwater　flexible　conductors　that　possess　mechanical　robustness,　adhesion,　and　self-healing　properties　remains　a　challenge.　Herein,　hydrophobic　interaction　is　combined　with　electrostatic　interaction　to　obtain　a　solvent-free　transparent　poly(ionic　liquid)　elastomer　(PILE)　fabricated　using　soft　acrylate　monomers　and　acrylate　ionic　liquids.　The　synergy　of　hydrophobic　and　electrostatic　interactions　can　eliminate　the　hydration　of　water　molecules　underwater,　giving　the　PILE　adjustable　fracture　strength,　good　elasticity,　high　stretchability,　high　toughness,　fatigue　resistance,　underwater　self-healing　ability,　underwater　adhesion,　and　ionic　conductivity.　As　a　result,　the　transparent　iontronic　sensor　generated　from　the　PILE　can　achieve　multifunctional　sensing　and　human　motion　detection　with　high　sensitivity　and　stability.　In　particular,　the　sensor　can　also　transmit　information　underwater　through　stretching,　pressing,　and　non-contact　modes,　demonstrating　its　huge　potential　in　underwater　flexible　iontronic　devices.　©　2023　Wiley-VCH　GmbH.