The purpose of this study was to determine the optimal mixing conditions of three different amounts of seatangle powder, sugar, and butter in germinated brown rice cookie prepared with seatangle powder. The experiment was designed according to the Central Composite Design of response surface, which showed 16 experimental points including 2 replicates for seatangle powder, sugar and butter. The mechanical and sensory properties of each test were measured, and these values were applied to the mathematical models. A canonical form and perturbation plot showed the influence of each ingredient on the final product mixture. The L value, a value and b value decreased with increasing seatangle powder content and increased with sugar content. The a value and b value increased with increasing butter content, whereas the L value decreased with increasing butter content. Hardness decreased with increasing butter content. The results of sensory evaluation showed very significant values for texture (p<0.001), taste (p<0.01), and overall quality (p<0.05). As a result, the optimum formulation by numerical and graphical methods was calculated to be seatangle powder 4.25 g, sugar 49.86 g, and butter 58.23 g.