Objective To investigate the changes of aquaporin 4(AQP4) and its mRNA expression in rat retina under different acute ocular hypertension ( AOH )，so as to study the role of AQP4 in some diseases related with the alteration of ocular pressure. Methods The AOH rat models were established by perfusing isotonic salt solution into the anterior chamber of rat eyes through a connected reservoir, which was situated at 75cm,125cm and 150cm heights to produce appropriate intraocular pressure. HE staining was performed to check the thickness and morphological changes of the retinal inner layers, and Nissl staining was used to count the number of ganglion cells in the ganglion cells layer (GCL). The changse of AQP4 and its mRNA expression in rat retina under different AOH were detected by immunofluorescence staining and confocal microscope，in situ hybridization and RTPCR respectively. Results The retina was swelling and the thickness of retina inner layer was improved under different AOH, and the number of ganglion cells in GCL was decreased after the perfusion stopped. The expressions of AQP4 and its mRNA in rat retina under different AOH were significantly elevated compared with the normal control groups. This upregulation expression had a strong correlation with the thickness changes of retinal inner layer and the decrease in the cell number of the GCL under different AOH. Conclusion The upregulation of AQP4 and its mRNA expression in rat retina was correlated with the increased intraocular pressure. The results indicate that AQP4 may play an important role in the pathophysiol