Aim To investigate the relationship between aquaporin-4(AQP4)mRNA expression and blood-brain barrier(BBB) permeability after experimental cerebral hemorrhage in rats. Methods The cerebral hemorrhage models were established by stereotaxic injection of auto-non-anticoagulant artery blood into the caudate nucleus.AQP4 mRNA expression was detected by RT-PCR,BBB permeability by Evens Blue method and brain water contents by dry-wet weight method. Results In contrast to the control group,AQP4 mRNA expression increased in cerebral hemorrhage group at 6 hours(1.06±0.12),reached peak at 3 days(1.34±0.14),then was still higher than normal at 7 days(p<0.05);BBB permeability increased at 6 hours after cerebral hemorrhage(0.5955±0.0956),reached peak at 1～3 days(0.8889±0.0968,0.7914±0.0520),and decreased at 5～7 days gradually(p<0.05).There was a significantly positive correlation between AQP4 mRNA expression and BBB permeability(r=0.686,p<0.01),which was consistent with the change of cerebral edema. Conclusion Cerebral edema may be formed through the upregulation of aquaporin-4 mRNA expression and the increase of BBB permeability after cerebral hemorrhage.