Purpose: The purpose of study was to investigate the quality characteristics and antioxidant activities of crackers with Ecklonia stolonifera. Methods: Crackers were prepared with different amounts (0, 2, 4, 6, 8%) of E. stolonifera powder and their physicochemical and sensory characteristic were examined. After extracting E. stolonifera with 70% ethanol, freeze-dried powder was used to measure total polyphenol, DPPH radical scavenging activity and reducing power. Results: In terms of quality characteristics, crackers containing 8% E. stolonifera showed the lowest pH value (6.68±0.02). The pH changed significantly with added amount. L-value (lightness), a-value (redness), and b-value (yellowness) were decreased with increasing concentration. Moisture content had significant decrease with added amount, and 8% additive had the lowest result. Hardness significantly increased as amounts of powder. Total phenolic content and reducing power of E. stolonifera were 17.90 mg GAE/g, and 0.28 O.D., respectively. DPPH free radical scavenging activity was 36.94%. Conclusion: The crackers containing 8% E. stolonifera yielded the highest antioxidant activation. Total phenolic content had the tendency to increase with more additive (p<0.001) DPPH free radical scavenging activity and reducing power showed significant growth with increasing concentration (p<0.001). Sensory evaluation indicated that the crackers containing 6% E. stolonifera was the most preferred in terms of color, flavor, taste, texture, appearance and overall acceptability. Based on these results, 6% additive seems most appropriate for good quality of E. stolonifera crackers.