Oxidation reactions on –OH groups at C-2 and C-3 positions of the uronic units of sodium alginate were performed with sodium periodate, and the influence of degree of oxidation on physical properties of the oxidized derivatives was analyzed. The aim of this work was to find new active functional groups on alginates, which is a polymer of interest as support in drug-controlled delivery systems. The molar mass decreases rapidly until an oxidation of 10 mol% and then remains nearly constant. Polymers with a degree of oxidation higher than 10 mol% were no more able to form gels with calcium ions. Both elastic modulus ( G′) and swelling degree (SD) of alginate gels decrease as the degree of oxidation increases. This behavior was attributed to the decreasing in the cooperative interactions between calcium ions and carboxylate groups due to a decrease in both the molar mass and the number of unreacted G units.