In this study, response surface methodology (RSM) was used to optimize the extraction parameters of dandelion root polysaccharide (DRP). Two novel polysaccharides (DRP-2b, DRP-3a) were isolated from dandelion root by graded ethanol precipitation and column chromatography. Structural analyses indicated that DRP-2b, with a molecular weight of 31.8 kDa, was composed of rhamnose, glucuronic acid, glucose, galactose and arabinose, whereas DRP-3a, with a molecular weight of 6.72 kDa, was composed of rhamnose, glucose, galactose and arabinose. The backbones of DRP-2b and DRP-3a were mainly composed of (1 → 5)-linked-α-D-Ara and (1 → 6)-linked-α-D-Glc, respectively. In addition, the antioxidant activities and protective effects against H2O2-induced damage in hepatic L02 cells were evaluated. DRP-3a exhibited higher radical scavenging activity than DRP-2b against the DPPH, hydroxyl and superoxide anions. Furthermore, DRP-3a exhibited strong protective effects against H2O2-induced damage in hepatic L02 cells. Thus, DRP-3a could be used as a potential antioxidant in medicine or as a functional food. Display omitted •RSM was successfully used for optimizing the extraction parameters of DRP.•Two new polysaccharides (DRP-2b, DRP-3a) were obtained from dandelion root.•Preliminary characterization of the two polysaccharides was performed.•DRP-3a possessed stronger free radical scavenging ability than DRP-2b.•DRP-3a exhibited protective effects against H2O2-induced damage in L02 cells.