The quest to determine and use polyphenolic compounds present in fruits and vegetables as natural antioxidants has recently attracted much attention due to their beneficial health effects. In this study, the total polyphenol content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC), antioxidant activity (AA), and individual polyphenol components of Simon No. 1, Yuzi No. 7, Shangshu 19, and Pushu 32 sweet potato cultivars (edible parts: leaf, stalk, stem, skin, and flesh) were investigated. TPC, TFC, and TAC values ranged from 440 ± 0.17-12080 ± 0.58 CAE mg/100 g DW, 94 ± 0.08-4210 ± 0.74 QE mg/100 g DW, and 7 ± 0.01-1010 ± 0.54 CGE mg/100 g DW, respectively. Yuzi No. 7 sweet potato cultivar contained significantly higher amounts of TPC, TFC, TAC, and AA in all its edible parts, followed by Pushu 32, Simon No. 1, and Shangshu 19 in that order. Regardless of the sweet potato cultivar used, TPC, TFC, and TAC of sweet potato leaves were significantly higher than those of other edible parts. High-performance liquid chromatography revealed 19 individual phenolic compounds. In general, 3,5-di-O-caffeoylquinic acid, astragalin, and cyanidin were the predominant phenolic acid, flavonoid, and anthocyanin compounds, respectively. The correlation analysis suggested that higher AA could be attributed to higher polyphenol content. Based on our results, edible parts of Yuzi No. 7 sweet potato cultivar presented the highest amounts of polyphenol content and AA suggesting the possibility of utilizing this cultivar by farmers and the food industry as a functional food product.