The effect of gamma radiation on the physical-chemical properties of sodium alginate Algimar has been investigated. Dilution viscometry, densitometry, and FTIR spectroscopy served to identify modifications. Decreasing intrinsic viscosities clearly revealed chain cleavage for both solid alginate and alginate in aqueous solution. The invariance of the partial specific volume and infrared results indicate that chain degradation occurs without significant change of the chemical structure. The obtained results have practical implication in the field of radiation modification and sterilization of sodium alginate used for microcapsule formation.