Background: Seaweeds contain significant quantities of lipids, protein, vitamins and minerals. Aquavac Ergosan contains 1% alginic acid extracted from two brown seaweeds, Laminaria digitata and Ascophyllum nodosum. Both in vivo and in-vitro researches have mainly been focused on the effect of Ergosan on fish growth, survival rate, reproductive performance and innate immunity in blood and epidermal mucus. Despite numerous studies on the effects of Ergosan on immune system of aquatic animals and evaluation of seaweeds in proximate analysis, there is no data available on proximate analysis of irradiated Ergosan extract (alginic acid). Therefore, the aim of this study was to assess the effect of on different groups of irradiated alginic acid (10, 20, 30, 40 and 50 KGy) for analyzing proximate composition. Materials and Methods: Alginic acid was prepared from the sonicated Ergosan extract. The Alginic acid extracted from Ergosan was irradiated with a gamma cell. The protein and lipid content and Moisture and ash were recorded. Results: Statistical analysis showed no significant differences among all of groups in terms of protein, lipid, ash and moisture. Conclusion: Radiation processing is a very convenient tool for imparting desirable effects in polymeric materials. The polysaccharide degradation by gamma or ultraviolet irradiation is free of initiators. High energy radiation technique can be effectively used to decrease the molecular weight of different polysaccharides such as alginate and Chitosan. Based on the results of this study, gamma irradiation of alginic acid as natural polysaccharide had no effect on crude protein, crude lipid, moisture and ash.