This study was performed to examine the optimum addition amount of Hizikia fusiformis powder to be used with rice flour in the preparation of Hizikia fusiformis Sulgidduk (traditional rice cake). Hizikia fusiformis powder was added to rice powder at ratios of 5, 10, 15 and 20% (w/w). The moisture content of Sulgidduk was increased with the addition of Hizikia fusiformis powder, whereas the pH content was decreased. The addition also lowered the lightness and yellowness values but increased the greenness value. Mineral contents were increased. Hardness, springiness, and brittleness were decreased, and cohesiveness was increased as the added powder content also increased. In the sensory evaluation of Hizikia fusiformis Sulgidduk, color, flavor, taste, softness, chewiness, moistness, cohesiveness, and overall acceptability characteristics were all highest at the 10% addition level. Thus it can be proposed that this is the ideal level of Hizikia fusiformis addition in terms of the sensory properties of the cooked product.