Apelin-13 is a novel adipocytokine participating in diabetes, but its role in diabetic retinopathy (DR) is still unknown. This study aimed to investigate the effect of apelin-13 on proliferative potential in DR and its antagonist inhibitory effects. Localization of apelin-13, GFAP and VEGF was detected by immunofluorescence in Müller cells and retina of diabetic rats. The effects of apelin-13 on cell function were assessed by MTT, spreading assay, apoptosis and Boyden chamber assay in vitro. Additionally, the mRNA and protein of apelin-13, GFAP and VEGF in cultured Müller cells and retina of diabetic rats were measured by real-time PCR and western blot. Apelin-13 antagonist F13A was used to block apelin-13 and to study its effects in vivo and vitro. Strong staining of apelin-13, co-localized with GFAP and VEGF, was observed in the retina of diabetic rats. Apelin-13, GFAP and VEGF mRNA and protein levels were significantly increased in retinas of diabetic rats and Müller cells under hypoxia. Moreover, exogenous apelin-13 promoted retinal Müller cell proliferation in vivo, and induced cell proliferation, migration, spreading and survival in vitro. Simultaneously, apelin-13 induced GFAP and VEGF expression. Inversely, F13A markedly reduced the retinal gliosis caused by diabetes. Furthermore, F13A suppressed both GFAP and VEGF expression in vivo and vitro. This study indicated apelin-13 play an important role in the development of DR. Apelin-13 antagonist could inhibit gliosis in retina of diabetic rats and proliferation of cultured Müller cells under hypoxia, which present a potential therapeutic target for the DR.