AbstractFucoidan powder was added in amounts of 0.05, 0.1,0.3, and 0.5% to sour cream butter and sensory and chemical properties were tested on their shelf life for 60 days during storage. Peroxide levels initially increased until day 40 of storage and then decreased. Butter samples from the control group had the highest amount of peroxide on day 40 (15.25 ± 1.41 meq/kg butter), while samples treated with fucoidan 0.5% had the lowest amount of peroxide (6.35 ± 0.53 meq/kg butter). The acidity of butter treatments increased during storage (p< .05). Butter samples from the control group had the highest acidity at 60 days of storage (0.40 ± 0.033 mg KOH / g butter), while samples treated with 0.5% fucoidan had the lowest acidity (0.17 ± 0.013 mg KOH / g butter). The treated butter samples showed the highest stability. Fucoidan, as an antioxidant, reduces the taste, odor, and discoloration of butter added with fucoidan during storage because it completely removes odorless tasteless powder, and the free radical chain is involved in oxidation and improves product properties. The results showed that there are no significant changes in the acceptance rate of butter treated with fucoidan during 60 days of storage in the refrigerator (p> .05). The sensory scores of the treated butter showed that the sensory properties during the storage period were similar to the control samples, but on day 40 of storage, they decreased. In general, a concentration of 0.5% fucoidan delays the oxidative process and increases shelf life and is selected as a superior treatment in terms of sensory evaluation, and is introduced as a functional food.