Response surface methodology (RSM) was used for the analysis and optimization of the production process of Kochujang added with Maesil extract. The process variables were the amount of Maesil extract ($0{sim}8%$) and red pepper powder ($6{sim}10%$). pH and all color characteristics (L*-, a*-, and b*-value) decreased but titratable acidity and water activity increased with the addition of Maesil extract. Amino nitrogen content appeared to decrease with the addition of red pepper powder. The highest sensory flavor score was obtained when 2.20% Maesil extract and 8.62% red pepper powder were blended, the highest sensory taste score with 6.63% Maesil extract and 9.50% red pepper powder, and the highest sensory color score with 7.80% Maesil extract and 8.62% red pepper powder respectively. The point chosen as representative of the optimal area corresponds to $X_1=3.60%,;X_2=10%;and;X_1=4.08%,;X_2=9.96%$ for physicochemical and sensory quality, respectively.