New amphiphilic polysaccharides with controlled structure were synthesized by coupling between a carboxylic function present on preformed polyester chains and a hydroxyl group naturally present on polysaccharides. First, the synthesis of poly(E-caprolactone) monocarboxylic acid (R-PCLCO2H) was carried out by ring-opening uncatalyzed polymerization of monomer in the presence of a carboxylic acid (R-CO2H). R-PCL-CO2H was then reacted with carbonyl diimidazole, and the resulting activated intermediate (imidazolide) was further reacted with dextran (Dex) at different molar ratios to obtain amphiphilic copolymers with various hydrophilic-lipophilic balance. The coupling reaction was followed by GPC, indicating a total conversion. The copolymers were further characterized by GPC, H-1 NMR, and FTIR. Nanoparticles of less than 200 nm, with potential interest for controlled release of bioactive compounds, were successfully prepared by using these new materials.