Protein particles are promising candidates for therapeutic delivery. In this study, we report a generalizable strategy to assemble a series of proteins into pH-cleavable protein particles that recover protein functionality after disassembly. Our strategy uses an acid-labile reversible cross-linker based on maleic anhydride chemistry, which allows the cross-linking of proteins and releases unmodified proteins upon cleavage, causing minimal loss of protein functionality. The protein particles can be rapidly disassembled at a mildly acidic pH (<6.5) and inside cells with negligible cytotoxicity. Furthermore, cleavage of the cross-linker led to above 97% recovery of enzymatic activity, as evidenced by using glucose oxidase. This facile and robust strategy to engineer pH-cleavable protein particles may provide a new platform for therapeutic protein delivery as well as for small molecule drug and nucleic acid delivery.