Background: The transient increase of intraocular pressure (IOP) following neodymium YAG laser capsulotomy can occur in a significant number of patients, which requires prophylactic treatment with IOP reducing drugs, and in some patients, postoperative IOP monitoring. This study was performed to compare the efficacy of brimonidine 0.2% versus latanoprost0.005% (Xalatan) in preventing the IOP elevation after YAG laser posterior capsulotomy in patients visiting ophthalmology clinic in Alavi Hospital.Methods: This study was a randomized, double-blind clinical trial that included 100 patients who had developed posterior capsule opacification (PCO) as a result of previous cataract surgery and were candidate for undergoing YAG laser posterior capsulotomy. The patients were randomly divided into two groups of 50 patients. One group received brimonidine 0.2% one hour before surgery, and the other group received Xalatan 0.005% in the night before laser surgery. In both groups the patients' IOP was measured in baseline, 1, 2, 3, 24 hours, 3 days and one week after surgery. The gathered data were analyzed using statistical methods in SPSS.16.Results: The mean IOP, 1, 2, 3, and 24 hours, 3 days, and one week after surgery didn't show any significant difference between two groups. IOP one hour before surgery changed significantly compared to one hour after surgery and a statistically significant relationship was found between the two groups, though at other times of measurement, the differences were not significant.Conclusions: Results showed that using Brimonidine 0.2% or Latanoprost 0.005% as prophylactic before YAG laser posterior capsulotomy could be effective in preventing IOP after treatment.