Hydrogen-fueled　and　hydrogen-hybridized　aircraft　engines　are　a　new　trend　in　the　aviation　industry　for　environmental　reasons.　Single　crystalline　Ni-based　superalloys　are　the　most　commonly　used　engine　materials　and　their　hydrogen　embrittlement　properties　need　urgent　investigation.　In　this　study,　the　hydrogen　embrittlement　behavior　and　underlying　fracture　mechanism　of　a　second-generation　Ni-based　single　crystal　superalloy　with　electrochemical　hydrogen　pre-charge　were　investigated.　The　superalloy　showed　tremendous　susceptibility　to　hydrogen　embrittlement　with　reduced　strength　and　ductility.　A　large　number　of　micropores　and　cracks　on　the　fracture　surface　are　found　in　hydrogen-charged　specimens,　leading　to　embrittlement　and　ultimate　cracking.　More　dislocations,　stacking　faults　and　DSBs　are　observed　in　specimens　with　hydrogen　uptake.　Hydrogen-induced　micropores　first　form　at　the　γ/γ′　interface　and　then　propagate　into　the　γ′　phase,　leading　to　cracking,　which　was　analyzed　using　in　situ　environmental　studies　with　a　transmission　electron　microscope.　Hydrogen　reduces　the　cohesive　strength　between　the　γ-　and　γ′-phase　and　accelerates　crack　propagation　along　the　voids.　Hydrogen　embrittlement　fracture　in　Ni-based　single　crystal　superalloys　is　due　to　synergistic　hydrogen-enhanced　local　plasticity,　strain-induced　vacancies　and　decohesion　in　the　hydrogen-induced　cracking　process.　©　2023　The　Authors