Irradiated red pepper powder (IRPP) was tested for its ability to retard fermentation and to maintain a high quality of Kimchi by the reduction of the initial microbial load. Kimchi containing IRPP at the doses of 0, 5, 10, 15, or 20 kGy was prepared. Quality indices for Kimchi in this study were pH, titratable acidity, reducing sugar content, total microbial count, lactic acid bacterial load, and sensory evaluation. Based on the pH and titratable acidity, the Kimchi with IRPP showed a retarded fermentation until 15 days. The number of the total aerobes and lactic acid bacteria of the Kimchi with IRPP were lower by about 1 log CFU/mL compared to control at day 0, however, the counts increased to 8.5 log CFU/mL after 10 days, which was similar to the control group. Kimchi that was fermented with 5 kGy IRPP was better than control and other treatments in odor and color, whereas the control scored highest in taste. Addition of IRPP showed a limited retardation of Kimchi fermentation without other quality deterioration.