The effects of A771726, the active metabolite of leflunomide, on experimental rat corneal neovascularization (NV) in vivo and on cultured human umbilical vein endothelial cells in vitro were studied. The corneal NV was induced by alkali burn in 40 SD rats. The rats were randomly divided into 4 groups with 10 rats in each group. Group A was treated with 0.9% sodium chloride (control group), and group B, group C and group D were given different concentrations of A771726 eye drops (0.5%,l.0%,2.0% respectively) 4 times daily during days 0-28. The occurrence and development of corneal NV were observed at 4,7,14,21 and 28 day after alkali burn by a slit lamp microscope. The cultured human umbilical vein endothelial cells (ECV-304) were incubated with A771726 solution at different concentrations (20,40,80,160,320μmol/L) for 36h. The proliferation of cells was assessed by methyl thiazolyl tetrazolium (MTT), and the expression of proliferating cell nuclear antigen (PCNA) in cells was detected by using immunofluorescence under the laser confocal microscope. The rat model showed that the onset of corneal NV was delayed and progression of corneal NV was inhibited in the groups C and D. The corneal NV areas in groups C and D were significantly smaller than in groups A and B (P0.05). A771726 solution (≥40μmol/L) could inhibit proliferation of human umbilical vein endothelial cells and decrease the expression of PCNA in cells significantly. A771726, as the active metabolite of leflunomide, strongly prevented corneal NV induced by alkali burn in the in vivo model, and inhibited proliferation of human umbilical vein endothelial cells in the in vitro model. Therefore, A771726 may serve as an angiogenic inhibitor in the treatment of corneal NV.