The kinetics of gelation between some heavy divalent metal ions and sodium alginate polysaccharide sol have been studied complexometrically at temperatures between 25 and 65 degreesC. Using a large excess of alginate sol concentration, the pseudo-first-order plots of exchange between Na+ counter ions of the macromolecular chains of alginate sol and the metal ions give sigmoidal curves with two distinct regions. The initial part was relatively fast and curved significantly at early times, followed by a slow decrease in the rates at longer times. The rate constants of gelation were found to show second-order overall-kinetics and first-order in the concentration of both reactants. The kinetic parameters have been evaluated and a consistent gelation mechanism is suggested.