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Selenium (Se)-enriched proteins are an important dietary source of Se for humans; however, only a few Se-enriched proteins have been identified. In the present study, we tested for potential antioxidant activity by Se-enriched soy protein, both in vitro and in vivo. Se-enriched soy protein isolate (S-SPI) was shown to have a higher free radical scavenging ability compared to ordinary soy protein isolate (O-SPI). Furthermore, Caco-2 cell viability was improved by S-SPI at low doses, whereas O-SPI did not. In addition, S-SPI was shown to inhibit oxidative stress via modulation of the NRF2-HO1 signaling pathway, upregulating the expression of downstream antioxidant enzymes (GPx, SOD). To further study the antioxidant capacity of S-SPI, BALB/c female mice were given oral gavages with 0.8 mL of S-SPI or O-SPI (5 g/kg/d, 20 g/kg/d and 40 g/kg/d) or saline as control. Hepatic GPx and SOD activity increased with increasing S-SPI dosage, but not with O-SPI. Taken together, our results suggest that Se-enriched soy protein has a high antioxidant ability and may be used as a dietary supplement for people with oxidative dam-age-mediated diseases.