Objective:To observe the nitric oxide synthase(NOS) expression in retina, and to investigate the function of the NOS inhibitor aminoguanidine(AG) in rats with acute intraocular hypertension. Methods:Twenty-seven SD rats were randomly divided into three groups:blank control(unoperational group),experimental group Ⅰ(ocular hypertension group),experimental group Ⅱ(drug-given group). Then each experimental group was divided into subgroups at 12 hours,24 hours,3 days and 7 days after perfusion,and NOS expression in the retina were detected by NADPH-diaphorase histochemistry. Results:The staining of NOS were localized in retinas of all groups. The count of NOS staining cells in the experimental group Ⅰ was more significant than that in the blank control. After AG was injected, the levels of NOS decreased. Conclusions:NO should play some cytotoxicity roles to retina. By inhibiting the activity of iNOS,AG might protect the retina against acute ocular hypertension injury.