While polymer-based sustained-release depots have been successfully used for a number of chemical and peptide drugs,there has yet to be a single product in this category for protein therapeutics (Nutropin Depot has been withdrawn).Due to conformational instability, proteins are easily denatured during the processes of formulation and in vivo release.For a practical technology, however, approaches to stabilize proteins must not compromise with undesired release kinetics (severe burst for example), excipient toxicity, and manufacture complicity.Here we introduce a unique system, stable polymer aqueous-aqueous emulsion, using which delicate proteins can be packed into fine polysaccharide glassy particles under a condition free of stability hazards (such as organic solvents, strong interfacial tension, cross-linking agents).Once loaded in the glassy particles, proteins are protected against organic solvents and hydrated environment, and can easily be incorporated into various polymeric devices with improved release kinetics.