The antioxidant properties and phenolic profiles were first investigated in this paper on the leaves of three red pepper cultivars, Blackcuban (BCPL), Hongjinju (HPL), and Yeokgang-hongjanggun (YHPL). Of the ethanol extract of the three cultivars, BCPL showed potent antioxidant activities against the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) and the 2,2-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical. Nine antioxidative compounds from the red pepper leaves were isolated and identified as one polyamine phenolic conjugate, N-caffeoylputrescine (1); three chlorogenic acid derivatives, 5-O-caffeoylquinic acid (2), 5-O-caffeoylquinic acid methyl ester (4), and 5-O-caffeoylquinic acid butyl ester (9); one anthocyanin, delphinidin-3-[4-trans-coumaroyl-l-rhamnosyl(1→6)glucopyranoside]-5-O-glucopyranoside (3); and four flavone glycosides, luteolin-7-O-apiofuranosyl(1→2)glucopyranoside (5), luteolin-7-O-glucopyranoside (6), apigenin 7-O-apiofuranosyl(1→2)glucopyranoside (7), apigenin-7-O-glucopyranoside (8). 1 and 3 had the greatest potential for radical-scavenging activity and HepG2 cells protecting effect against oxidative stress. BCPL exhibited the highest content of 1 and 3. Of the three cultivars BCPL may be considered a good source of antioxidants.