Correlations between oxidative stress and degenerative diseases have been gaining increasing attention. A number of studies affirm that exopolysaccharide (EPS) produced by lactic acid bacteria (LAB) can alleviate oxidative stress and further prevent the related diseases. In our previous study, Lactobacillus helveticus KLDS1.8701 has been shown to possess high antioxidant capacity in vitro. The aim of this study was to evaluate the ameliorative effects of EPS produced by L. helveticus KLDS1.8701 on oxidative stress. Firstly, EPS was isolated from the culture of L. helveticus KLDS1.8701 and purified using DEAE-Sepharose Fast Flow chromatography. Secondly, the antioxidant capacities of EPS fractions were evaluated using in vitro methods. Thirdly, an in vivo study was performed to investigate the possible protective effects of EPS on d-galactose (d-gal)-induced liver damage and gut microbiota disorder. In vitro antioxidant activity results suggested that EPS-1 exhibited strong scavenging properties on 2,2-diphenyl-1-picrylhydrazyl radical, superoxide radical, hydroxyl radical, and chelating activity on ferrous ion. In vivo, EPS-1 supplementation significantly attenuated oxidative status such as decreased organic index, liver injury and liver oxidative stress. EPS-1 supplementation shifted the gut microbiota composition to that of the control group. In addition, the analysis of Spearman's rank correlation suggested that the protective effects of EPS correlated with manipulating the gut microbiota composition in d-gal-induced mice. These results implied that EPS-1 supplementation could mitigate hepatic oxidative stress via manipulating the gut microbiota composition and be used as a potential candidate to attenuate oxidative damage.