Objective To investigate the expression, relationship, significance of cyclooxygenase-2 (COX-2) and malonic dialdehyde (MDA) after cerebral ischemic-reperfusion injury and provide basis of treatment. Methods The focal cerebral ischemic-reperfusion model was established with thread embolish of middle cerebral artery. Western blotting, barhituric acid method and neurological evaluation were used to examine the expression of COX-2, MDA in cortex and the changes of neurological function； TTC staining was used to observe the changes of cerebral infarction volume. Results COX-2 prorein expression was correclated well with the MDA（EM>r/EM>=0.910，EM>P/EM>0.01). The content of COX-2 and MDA was very low in sham operation group, they were increased significantly at I2h/R6h model group, with the increase of reperfusion time,they remarkably reached its peak at I2h/R24h,they were slightly lower at I2h/R48h, but still maintained at a high level;Compared with model group, in tetramethylpyrazine(TMP) treatment group, the content of MDA and cerebral infarction volume were markedly decreased（EM>P/EM>0.01). Conclusion The expression of COX-2 and MDA increases in cerebral ischemic-reperfusion injury.It indicates they may play an important role in the mechani