To understand ripening-dependent changes in phytonutrients, five commercial cultivars of red peppers (Capsicum annuum L.) grown in an open field in Taean, South Korea, were selected and their fruits were harvested at green mature (GM), intermediate breaker (BR), and red ripe (RR) stages and their phytonutrient contents and antioxidant activities were compared. Three major patterns in relation to ripening progress were observed. First, continuous increases were observed in vitamin C, total phenol, vitamin E (especially α-tocopherol), total free sugar, β-carotene, linolenic acid content, and antioxidant activity. Second, decreasing patterns were observed in phytosterols (campesterol, stigmasterol, and β-sitosterol) and linoleic acid. Third, total flavonoid and squalene contents were relatively higher at the BR stage compared with the GM and RR stages. These results indicate that each phytonutrient has a unique pattern of accumulation and degradation during the fruit-maturing process. Unlike the mentioned phytonutrients, which showed similar patterns in all tested cultivars, capsaicinoids exhibited quite different patterns of ripening-dependent changes among the cultivars. Throughout the ripening processes, positive correlations with antioxidant activity were observed in vitamin E (r = 0.814**), β-carotene (r = 0.772*), vitamin C (r = 0.610**), and total phenol (r = 0.595**) contents, whereas capsaicinoids, total flavonoid, and phytosterols exhibited no or slightly negative correlations. In conclusion, the ripening of red pepper fruits is accompanied by continuous increments in various phytonutrients and subsequent antioxidant activity.