Saururus chinensis (S. chinensis) has long been used in traditional medicine for its diverse pharmacological activities. This study aimed to establish an optimized extraction and fractionation process for S. chinensis and evaluate its antioxidant efficacy based on its major bioactive lignans, sauchinone and manassantin B. Quantitative analysis using high performance liquid chromatography (HPLC) exhibited excellent linearity (R² = 0.9994) for both compounds. Among the extraction methods and solvents tested, the reflux extraction with 100% ethanol yielded the highest contents of sauchinone (2.576%) and manassantin B (2.066%). In successive solvent fractionation, sauchinone and manassantin B were selectively concentrated in the n-hexane (9.862%) and dichloromethane (10.480%) fractions, respectively. To evaluate antioxidant activities, reactive oxygen species (ROS) and peroxynitrite (ONOO^-) scavenging assays were performed. Both standards and 100% ethanol reflux extract concentration-dependently exhibited potent scavenging activities. Notably, while the n-hexane and dichloromethane fractions showed strong ONOO^- scavenging activities, the ethyl acetate fraction exhibited the highest ROS scavenging activity. These results indicate that the optimized extraction process can efficiently secure active antioxidant components, and S. chinensis extracts hold significant potential as functional ingredients for cosmetics, health foods and natural pharmaceuticals.