The free oxygen radical scavenging effects of agar oligomers were studied by the method for determination of Luminesecence and DPPH assay. The results showed that agar oligomer ML had strong scavenging effects on #OH and O2 #- , IC50 were 0. 05mg#mL- 1 and 0. 7mg#mL- 1, but the scavenging ef fect on DPPH radical was much lower than Vc and probuto l. Comparation of the scavenging activities on O2 #- between agar Oligomers with different sulphate content and molecular weight showed that high sulphate group or high molecular weight took the main action to scavenge radicals. Agar oligomers taken ig to LPS+ D- GalN induced liver injury mice could effectively inhibit the inrease of GPT acticity and MDA content , and maintain the acitivities of SOD、GSH- Px activity in mice serum. It had good protective effect on liver injury.