The seaweed Hizikia fusiformis is rich in protein, carbohydrates, vitamins, and minerals. We investigated the physicochemical properties and antioxidant activities of yanggaeng made with agar, sugar, honey, oligosaccharide, cooked white bean paste, and different amounts (0, 1, 2, 3, 4, and 5%) of H. fusiformis powder. The proximate composition, pH, sugar content, color, texture, antioxidant activity, and sensory properties of the yanggaeng were investigated. The moisture and sugar contents of the yanggaeng did not change despite increasing the amount of H. fusiformis. The pH decreased with increasing H. fusiformis. The lightness decreased significantly, whereas the redness and yellowness increased with increasing amounts of H. fusiformis. In the texture profile analysis, the hardness, gumminess, and chewiness decreased with increasing H. fusiformis content. The antioxidant activity of the yanggaeng increased with the concentration of the H. fusiformis powder. The yanggaeng containing 2% H. fusiformis had the highest overall sensory acceptance score. The addition of H. fusiformis to yanggaeng appears to improve its quality and antioxidant activity.