This study was performed to determine the optimal manufacturing conditions of cookies prepared with Hizikia fusiformis. The variables in Hizikia fusiformis cookies production were the amounts of Hizikia fusiformis powder, butter, and sugar. Six sensory characteristics were used for sensory evaluations, including color, appearance, taste, brittleness, hardness, and overall acceptability. The optimal amounts of the three variables were found to be 6.00 g for Hizikia fusiformis powder, 100.00 g for butter, and 70.00 g for sugar against flour powder 200 g, which satisfies a target sensory score (7.0/9.0) according to the response surface method. Cookies with these optimal amounts of Hizikia fusiformis powder, butter, and sugar were tasted by 114 consumers and showed a high acceptability score (7.21). Females preferred the flavor of Hizikia fusiformis significantly more than males did (p<0.05). Older consumers (${geq}30$ years old) scored significantly higher than younger consumers (${leq}29$ years old) in texture (p<0.05). Spread ratio and hardness scores of Hizikia fusiformis cookies were lower than those of control cookies. Color analysis results of Hizikia fusiformis cookies were significantly lower in brightness and redness, and higher in yellowness than control cookies (p<0.01).