All aqueous multiphase systems have attracted significant attention recently, in particular water-in-water Pickering emulsions. In here, polydopamine nanoparticles (PDP) are investigated as stabilizers for dextran and poly(ethylene glycol) (PEG)-based aqueous emulsions. Remarkably, stable emulsions are obtained from the all-biocompatible materials that can be broken either via dilution or surfactant addition. Further cross-linking of PDP via poly(acrylic acid) and carbodiimide strengthens the stability of emulsion droplets in a colloidosome-like structure. After cross-linking, demulsification via dilution or surfactant addition was largely hindered. The PDP-mediated formation of all aqueous emulsions is expected to be generalized to different types of water-in-water emulsions with other polymers and offers new opportunities in surface modification as well as microencapsulation.