The critical behavior of relative viscosity and intrinsic viscosity near the gelation point was experimentally examined for 1 g/100 m/ alginate solution induced by cupric ions. The critical exponent of relative viscosity was found to be 1.27, which is in good agreement with the prediction of the percolation model based on a Rouse cluster approximation gives the exponent as 1.3. Critical behavior of intrinsic viscosity reveals that the constant of Huggins equation k’ for alginate clusters formed near the gelation point was considerably higher than that of linear alginate polychains in aqueous solution. Typically intramolecular crosslinking between polychains in the low cupric concentration could be detected in the plots of [eta] vs molar fraction of cupric ions for the system. The weak divergence of intrinsic viscosity resembles the critical behavior of Zimm clusters predicted by the three-dimensional percolation theory rather than clusters of classical theory.