The technical enzymatic hydrolysis lignin (EHL) and alkali lignin (AKL) were pretreated via alkaline depolymerization and organic solvent extraction process, respectively. The molecular weight of lignin was lowered and the molecular weight distribution was narrowed, while the content of phenolic hydroxyl group increased after the pretreatment of alkaline depolymerization or solvent extraction. The lignin extracted with ethyl acetate got the lowest molecular weight and highest phenolic hydroxyl group content, showing even better free radical scavenging ability than the commercial Irganox1010. Lignin/SBS elastomer composites were prepared with even dispersion of lignin in the SBS matrix with an average particle size close to 40 nm. It was demonstrated that the alkali lignin extracted with ethyl acetate showed the best improvement on the antioxidant performance of SBS and was comparable to that of Irganox1010 in the SBS elastomer, showing great application potential.