Marine　mussels　harness　catechol-rich　foot　proteins　with　hierarchically　assembled　nanostructures　to　achieve　robust　adhesion　in　the　dynamic　underwater　environment.　Herein,　mimicking　the　chemical　composition　and　hierarchical　nanostructure　of　mussel　foot　proteins,　a　silk-based　sealant　(named　SFT)　with　superior　wet　adhesion　and　instant　hemostasis　was　developed　by　introducing　tannic　acid　(TA)　into　silk　fibroin　(SF).　The　presence　of　TA　containing　abundant　phenolic　moieties　triggered　the　conformational　transition　of　SF　from　random　coil　to　β-sheet　and　the　hierarchical　assembly　of　nanofibrillar　structures,　imparting　SFT　with　high　intrinsic　toughness　(123.1　kJ　m-3).　The　phenolic　moiety,　with　strong　binding　affinity　to　nucleophiles　in　tissue　biomolecules,　also　endowed　SFT　with　tough　adhesion　to　wet　tissues　(strength　≈134.1　kPa)　even　in　the　presence　of　blood　and　robust　tissue　motions　(e.g.,　bleeding　heart)　and　exhibited　instant　hemostatic　capability　(within　30　s).　Given　the　unprecedented　combination　of　tough　adhesion　and　instant　homeostasis,　the　engineered　SFT　can　fulfil　unmet　challenges　and　serve　as　a　promising　surgical　sealant　for　suturelessly　sealing　ruptured　tissues　in　wet　and　dynamic　biological　environments.　©　2019　The　Royal　Society　of　Chemistry.