An in vitro digestive system simulates the human digestive tract. This study aimed to evaluate antioxidant activity and oxidative stability of roasted buckwheat extracts after treatment with an in vitro digestive system. The buckwheat samples were subjected to the following roasting conditions: 180℃ for 10 min, 180℃ for 20 min, 200℃ for 10 min, and 200℃ for 20 min; ethanol extracts of the buckwheat samples were prepared after the in vitro digestive system treatment. Buckwheat samples roasted at 200℃ for 10 min showed the highest in vitro antioxidant activities, including 2,2-diphenyl-1-picrylhydrazyl, 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) cation radical-scavenging activity, and ferric-reducing antioxidant power. The total phenolics content of buckwheat roasted at 200℃ for 10 min was 13.14 µmol tannic acid equivalent/g extract, while those of the samples subjected to the other roasting treatments ranged from 7.58 to 9.86 µmol tannic acid equivalent/g extract. Furthermore, the synthesis of primary and secondary oxidative products from corn oil containing 1,000 ppm buckwheat roasted at 200℃ for 10 min decreased by 10% and 20%, significantly, compared to those in the control groups (p<0.05). Overall, the ethanolic extracts of roasted buckwheat obtained after in vitro digestive treatment still possessed relatively high in vitro antioxidant activity. It was found that roasted buckwheat according to in vitro digestion could be used as an antioxidant material.