To suppress the gas forming caused by some yeast in the pack of traditional kochujang prepared at Sunchang area, which is the most severe problem during distribution of commercial products, mustard or horseradish powder as natural preservatives was mixed to the ingredients of kochujang and left for fermentation in clay pot as commercial scale for 180 day. The composition changes including quality and gas formaing in the kochujang containing those additives were monitored physicochemically and organoleptically. The fermented kochujang containing those additives were monitored physicohemically and organoleptically. The fermented kochujang containing 0.6% of horseradish showed lower organic acid content than that of the control but amino type nitrogen content, which is one of the important quality reference of kochujang, was higher in the one containing 0.6% natural preservatives. No color changed in the kochujang containing mustard but L and a value were increased in the kochujang containing horseradish. No difference of free reducing sugars was showed by the addition of those natural preservatives and the addition of 0.6% horseradish to kochujang had completely stopped gas forming during fermentation. The overall quality of the kochujang containing 0.6% horseradish was superior than that of the other treatments.