In this study, we examined the effects of different concentrations of red pepper seed (0%, 1%, 3%, 5%, and 7%) on pH, total acidity, color, reducing sugar content, total microbes, lactic acid bacteria, and sensory quality, in terms of prolonging the shelf-life of kimchi. The additions of red pepper seed resulted in higher pH levels, while total acidity was lower than that of the control. The kimchi with red pepper seed had higher reducing sugar contents than the control. Furthermore, the kimchi with red pepper seed showed higher b-values than the control. During fermentation, the amounts of lactic acid bacteria and total microbes were higher in the kimchi with red pepper seed than in the control, and the higher ratios resulted in higher quality kimchi. The additions of red pepper seed also resulted in changes of color, flavor, taste, and texture, having a large influence on overall product quality. In conclusion, in terms of preservation and consumption, the 3% and 5% red pepper seed concentrations offered enhanced shelf-life and better quality kimchi products.