The antioxidant activity of methanol extracts from five different parts (flesh, peel, core, seed, calyx) of Jangseong Daebong persimmon (Diospyros kaki cv. Hachiya) were evaluated by determining total phenol content (TPC), DPPH radical scavenging activity (RSA), ABTS RSA, and reducing power (RP). The flesh extract gave the highest yield (92.93%) while the lowest yield was obtained from the seed (5.17%). The seed extract showed the highest total phenolic content ($76.47pm0.009$ mg GAE/g extract), DPPH RSA ($IC_{50}=52.05pm1.61;{mu}g/mL$), ABTS RSA ($IC_{50}=30.94pm0.41;{mu}g/mL$) and RP ($IC_{50}=87.94pm0.37;{mu}g/mL$). In addition, the calyx extract also showed high antioxidant activity. On the other hand, the core extract gave the lowest TPC and all antioxidant assays. In particular, HT-29 cells showed extensive cell death when treated with $500;{mu}g/mL$ of calyx extracts. Thus, these results suggest that methanolic extracts of Jangseong Daebong persimmon seed and calyx may serve as a potential source of natural antioxidant for food and nutraceutical application.