Objective To increase the production of exopolysaccharides (EPS) from lactobacillus by optimizing fermentation conditions and evaluate the antioxidant activity of the extracted EPS. Methods P1-10 was isolated as a high yield EPS producing lactobacillus from kefir grains and identified by 16S rDNA sequencing. Meanwhile, the effects of carbon source composition and content in the medium and fermentation time on the EPS yield of P1-10 were investigated and compared. Additionally, scanning electron microscopy and in vitro antioxidant study was studied from the obtained EPS as well. Results Among the 12 kinds of isolated strains from kefir grains, P1-10 formed gram-positive colonies under microscopic examination after Gram staining, could coagulate milk, and had a string length greater than 15 mm. It was identified as Pediococcus acidilactici strain (MH143596.1 Pediocuccus acidilactici strain D15) by 16S rDNA sequencing and the maximum content of EPS was 6.52 mg/mL. In addition, the optimal conditions for P1-10 were obtained under the condition of MRS (DeMan-Rogosa-Sharpe medium) medium with the carbon source replaced by 40 g/L sucrose and fermenting at 35 ℃, pH 6.0 for 60 hours, while the highest yield of EPS was 29.09 mg/mL. Furthermore, the surface of EPS under the scanning electron microscopy was relatively rough, with a sense of layering and different sizes voids. Moreover, the elimination rates of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) free radicals in the 1.0 mg/mL vitamin C (vitamin C, VC), EPS and fermentation supernatant were 86.21%, 95.03%; 81.32%, 93.91% and 58.54%, 65.73%, respectively. Conclusion P1-10 can effectively increase the extraction efficiency of EPS compared to the normal culture with the optimizing of the culture conditions. As for the in vitro antioxidant experiments, EPS is indicated a strong ability to scavenge free radicals and antioxidant capacity due to the highly DPPH and ABTS radical scavenging rates. This study may provide a theoretical basis for the screening, extraction and functional activity research of EPS from lactic acid bacteria.