Biosourced Pickering emulsion stabilizers with stimuli responsiveness are mostly designed for recycling and do not offer fast degradability as required for drug-delivery applications. Herein, dextran-a hydrophilic and biofriendly polysaccharide obtainable from biomass recovery-was used for the first time as a brick material for the formulation of (bio)degradable pH-sensitive Pickering emulsions. It was first modified with hydrophobic acetal moieties to provide pH-sensitive acetalated dextran. Under acidic conditions, it degrades into three biocompatible (macro)molecules: dextran, ethanol, and acetone. Nanoparticles of acetalated dextran were obtained using the nanoprecipitation process and could be similarly fully hydrolyzed under acidic conditions within 6 h. Then, O/W Pickering emulsions of dodecane (model oil) and medium-chain triglyceride (biocompatible oil) were successfully stabilized using these nanoparticles. pH-induced destabilization of these Pickering emulsions (including nanoparticles degradation) took less than 24 h. Finally, neither accumulation of nanoparticles nor harmful component release happened during the process, making this stimuli-responsive vector safe and environmentally friendly.