Applying a dialysis process, new nanoparticles based on well-defined dextran esters of furan-2-carboxylic- and pyroglutamic acids were prepared, which can undergo cross-linking by UV irradiation. The highly functionalized products (total DS > 2) avoid the collapse of nanoparticles due to the prevention of hydrogen bond formation. The major fraction of the dextran ester nanospheres exhibits narrow size distribution down to 250 nm as mean diameter investigated by SEM.