Abstract: The objective of the research was to analyze the structure of the selenizing peptidoglycan (Se-PG) and examine the antioxidant capacity. Selenizing peptidoglycan was prepared by using Bacillus subtilis peptidoglycan and HNO₃-Na₂SeO₃. The properties of structural changes were analyzed by UV, FT-IR and NMR. Taking scavenging effects on DPPH, ABTS and·OH free radicals as indicators, the antioxidative function of raw materials and selenium-modified products were evaluated in vitro. The results showed that the selenium content was 369.32 μg/g and a new absorption peak appeared at 890 cm^-1 FT-IR spectroscopy in Se-PG, which was due to the form of selenite ester in Se-PG. Compared with the Na₂SeO₃ and PG, the DPPH, ABTS and·OH scavenging rates of Se-PG were increased, showing a concentration-dependent. When the concentration reached 5 mg/mL, the radical scavenging rates were the highest, which were 39.51%±0.26%, 39.47%±0.98%, and 48.38%±1.42%, respectively (P<0.05). The structural characterization showed that the PG had been successfully selenized, selenidation did not change the basic structure of PG and the Se-PG, and selenization showed an excellent ability in scavenging free radicals in vitro. Therefore,Se-PG could be used as potential antioxidants in the development of functional products.