AIM: To investigate biological effects of transthyretin (TTR) on the development of neovascularization under simulated diabetic retinopathy (DR) condition associated with high glucose and hypoxia. METHODS: Human retinal microvascular endothelial cells (hRECs) were cultured in normal and simulated DR environments with high glucose and hypoxia. The normal serum glucose concentration is approximately 5.5 mmol/L; thus, hyperglycemia was simulated with 25 mmol/L glucose, while hypoxia was induced using 200 μmol/L CoCl2. The influence of TTR on hRECs and human retinal pigment epithelial cells (hRPECs) was determined by incubating the cells with 4 μmol/L TTR in normal and abnormal media. A co-culture system was then employed to evaluate the effects of hRPECs on hRECs. RESULTS: Decreased hRECs and hRPECs were observed under abnormal conditions, including high-glucose and hypoxic media. In addition, hRECs were significantly inhibited by 4 μmol/L exogenous TTR during hyperglycemic culture. During co-culture, hRPECs inhibited hRECs in both the normal and abnormal environments. CONCLUSION: hREC growth is inhibited by exogenous TTR under simulated DR environments with high-glucose and hypoxic, particularly in the medium containing 25 mmol/L glucose. hRPECs, which manufacture TTR in the eye, also represses hRECs in the same environment. TTR is predicted to inhibit the proliferation of hRECs and neovascularization.