Sprouting is one of the processing methods to enhance bioavailability of some nutrients of agricultural products. Soybeans were germinated for 6 days and soybean (SB), soybean sprout (SBS), cotyledon of soybean sprout (CSS), and hypocotyl and root of soybean sprout (HRSS) were collected. Isoflavone profiles and in vitro antioxidant activities of 80% ethanol extracts of samples were analyzed. In addition, oxidative stability of the extract was evaluated in corn oils heated at 100 °C. The hypocotyl and root part of soybean sprout contained significantly (P < 0.05) higher content of isoflavone aglycones than the cotyledon part of soybean sprout. Diphenyl‐1‐picrylhydrazyl radial and 2,2’‐azinobis(3‐ethylbenzothiazoline‐6‐sul‐fonic acid cation radical scavenging activities of SBS were 1.6 and 1.3 times higher than those of SB, respectively (P < 0.05), whereas those of CSS were 1.1 and 1.8 times higher than those of HRSS, respectively (P < 0.05). CSS had higher ORAC and FRAP values than others. High correlations between contents of total flavonoids and antioxidant activities were observed in all in vitro antioxidant assays. SBS, CSS, and HRSS had significantly higher oxidative stability than SB in 100 °C heated corn oil after 9 hr treatment (P < 0.05). Generally, 80% ethanol extract of CSS had high in vitro antioxidant properties whereas HRSS had high aglycone forms of isoflavones. Isoflavone aglycones may not be major ingredients providing antioxidant activities of soybean sprout. Practical Application Soybeans are important crops for the preparation of tofu, soymilk, and protein sources. Soybean sprout prepared by germinating soybean and growing for several days is one of important food materials used as daily diet in some countries. In this study, antioxidant activities of different parts of soybean sprouts were evaluated using in vitro methods and bulk oil model systems. In addition, isoflavone profiles of soybean sprouts were determined. Enhanced antioxidant activities of soybean sprouts may help consumers choose healthier foods and extend business areas of the soybean food industry.