Embrittlement　of　polycrystalline　aluminum　by　liquid　gallium　represents　a　classic　example　of　liquid　metal　embrittlement,　whereas　the　interfacial　atomic　structure　of　Ga　penetration　front　remains　elusive　despite　decades　of　investigation.　We　performed　aberration-corrected　scanning　transmission　electron　microscopy　characterization　to　uncover　the　atomistic　structure　of　Ga-enriched　complexion　within　Al　general　grain　boundaries.　Multiple-layer　adsorption　of　Ga　with　ordering　gradients　is　revealed,　consisting　of　disordered　Ga　layers　at　the　GB　core　that　are　sandwiched　by　two　more　ordered　adsorbate　layers　connecting　to　both　aluminum　grains.　The　ordering　gradients　within　the　interfacial　complexion　are　further　verified　by　the　hybrid　Monte　Carlo　and　molecular　dynamic　simulations.　This　study　advances　our　fundamental　understandings　of　complexion　structures　within　general　grain　boundaries.　©　2021