Grafting of poly(N-vinylcaprolactam) side chains onto a hydrophilic dextran backbone was found to provide the dextran with new, thermoresponsive properties in aqueous solutions. Depending on its solution concentration, the resulting dextran derivative could exhibit a temperature-induced phase-transition and critical transition temperature (T(c)). Different anions and cations of added salts, including five potassium salts and five alkali-metal chlorides, were observed to influence the T(c) value of its aqueous solution. Except for potassium iodide, all added salts were found to lower the T(c) value. The addition of the surfactant, cationic cetyltrimethylammonium bromide or anionic sodium dodecyl sulfate, resulted in an increase of the T(c) value. With the help of the Coomassie Brilliant Blue dye as a polarity probe, the formation of hydrophobic aggregates above the T(c) was revealed for this new dextran derivative in aqueous solution.