Intracellular protein delivery is critical to the development of protein-based biopharmaceuticals and therapies. However, current delivery vectors often suffer from complicated syntheses, low generality among various proteins, and insufficient serum stability. Herein, we developed an enlightened cytosolic protein delivery strategy by dynamically crosslinking epigallocatechin gallate (EGCG), low-molecular-weight polyethylenimine (PEI 1.8k), and 2-acetylphenylboric acid (2-APBA) on the protein surface, hence forming the EPP-protein nanocapsules (NCs). EGCG enhanced protein encapsulation via hydrogen bonding, and reduced the positive charge density of PEI to endow the NCs with high serum tolerance, thereby enabling effective cellular internalization in serum. The formation of reversible imine and boronate ester among 2-APBA, EGCG, and PEI 1.8k allowed acid-triggered dissociation of EPP-protein NCs in the endolysosomes, which triggered efficient intracellular release of the native proteins. Such strategy therefore showed high efficiency and universality for diversities of proteins with different molecular weights and isoelectric points, including enzyme, toxin, antibody, and CRISPR (clustered regularly interspaced short palindromic repeats)-Cas9 ribonucleoprotein (RNP), outperforming the commercial protein transduction reagent PULSin and RNP transfection reagent lipofectamine CMAX. Moreover, intravenously (i.v.) injected EPP-saporin NCs efficiently delivered saporin into 4T1 tumor cells to provoke robust antitumor effect. This simple, versatile, and robust cytosolic protein delivery system holds translational potentials for the development of protein-based therapeutics.