Objective To investigate the relationship of oxidative damage with the secondary lesion in acid-burnt cornea. Methods The model of mild, moderate and severe acid burn in rat cornea was established in 72 Long-Evans rats. Four served as normal control. The content of corneal malonaldehyde (MDA) was determined by thiobarbituric acid test (TBA) and the activity of corneal superoxide dismutase (SOD) was detected by chemical colorimetry test at day 1, 3, 7, 14, 21, 28 after acid burn. Results No obvious change of MDA and SOD in the mildly-burnt cornea, MDA increased slightly and SOD was of no obvious change in the moderately-burnt cornea, MDA increased and SOD decreased in the severely-burnt cornea significantly. Conclusion The breakage of the balance between the generation and elimination of free radical is possible reason why the secondary lesion occurs in severely-burnt cornea.