Brain edema is a major importance in the pathophysiology of CNS injuries including stroke. Ischemic brain edema results from both cytotoxic edema, which is severe in astrocytes at early stage, and vasogenic edema caused by excessive blood-brain barrier (BBB) permeability. The present study was performed to determine the effect of Rhei Rhizoma on brain edema induced by middle cerebral artery occlusion (MCAO) in the rats. The neurological symptom, total infarct volume and edema index caused by MCAO were measured. The changes of Matrix Metalloproteinase-9 (MMP-9) and inducible nitric oxide synthase (iNOS) immunoreactivities were also observed. We found that Rhei Rhizoma extract improved the neurological symptom and attenuated the total infarct volume and brain edema caused by ischemic insult. Rhei Rhizoma extract also attenuated the expression of MMP-9 and iNOS. This results suggest that Rhei Rhizoma has a protective effect on the brain edema caused by ischemic insult.