The purpose of this study was to investigate the antioxidative effect and quality characteristics of cookies made with Sea tangle powder(STP). The cookies were at $30^{circ}C$ for 45 days. The 3% STP had higher pH value compared to the other groups and control. As more STP was added, the L-value and b-value decreased, and the a-value increased for the color values. The results of sensory evaluation and acceptance test showed that the cookies with 3% STP was significantly more preferable in overall acceptability than the others. The acid value, peroxide value, and thiobarbituric acid value were lower in cookies with 3% and 6% STP than in those cookies made 9% STP and the control cookies.