The purpose of this study was to find out the optimal mixing ratio of green tea powder, sugar, and water for the preparation of Seolgiddeok through Response Surface Methodology based on the color, sensory, and texture test. The oganoleptic and textural properties of Seolgiddeok prepared with various concentrations of green tea powder (0% (control group), 0.5% (GT-0.5 group), 1% (GT-1.0 group), 1.5% (GT-1.5 group), 2% (GT-2.0 group)), and their quality changes during storage were also investigated. The optimal mixing ratio of green tea powder, sugar, and water for preparing the best quality Seolgiddeok was 1.0%, 12%, and 22%, respectively. The proximate composition of green tea powder was 21.70% of crude protein, 8.49% of crude lipid, 2.95% of reducing sugar, and 6.40% of ash. The contents of crude lipid, reducing sugar, and catechins in Seolgiddeok added with a green tea powder were increased with increasing the content of green tea powder. The hardness and gumminess of GT-1.0 group were the lowest among four groups, whereas GT-1.0 and GT-2.0 groups had the lowest cohesiveness. While the control group was the lowest in adhesiveness, the springness was not significantly different among all groups. GT-0.5 and GT-1.5 groups were the highest in sweet taste and colorfulness, respectively. However, GT-1.0 group had the best overall quality. Total microbial numbers, the acidity and pH in Seolgiddeok during storage were decreased with increasing green tea powder content, and especially those of GT-1.0 and GT-1.5 groups were relatively the lower than others. The “L” value (lightness) of the control group (no additives) was the highest among five groups, and the value was decreased with storage period, and especially GT-0.5 groups had the lowest brightness. The“a”value (reddness) of the control group was the highest, followed by GT-0.5, GT-1.0, GT-1.5, and GT- 2.0 group in order. The“b”value (yellowness) was increased with the increase of green tea powder content. Above results indicated that GT-1.0 group showed the best quality of Seolgiddeok through organoleptic and rheology tests.