AIM: To identify the effects of interleukin (IL)-13 on retinal pigment epithelial (RPE) cells and the IL-13 level in aqueous humor of age-related macular degeneration (AMD) patients. METHODS: IL-13 levels in aqueous humor specimens from AMD patients were detected with enzyme-linked immunosorbent assay (ELISA). ARPE-19 cells were treated with 10 ng/mL IL-13 for 12, 24, and 48h. The cell proliferaton was evaluated by the MTS method. The mRNA and protein levels of α-SMA and ZO-1 were evaluated with quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot respectively. The expression of tumor necrosis factor-α (TNF-α), transforming growth factor-β (TGF-β) and vascular endothelial growth factor (VEGF) were assessed by ELISA. RESULTS: IL-13 levels in the aqueous humor of patients with AMD were significantly higher than those in the control (167.33±17.64 vs 27.12±5.65 pg/mL; P<0.01). In vitro, IL-13 of high concentrations (10, 15, and 20 ng/mL) inhibited ARPE-19 cell proliferation. α-SMA mRNA in ARPE-19 cell were increased (1.017±0.112 vs 1.476±0.168; P<0.001) and ZO-1 decreased (1.051±0.136 vs 0.702±0.069; P<0.001) after treated with 10 ng/mL IL-13 for 48h. The protein expression of α-SMA and ZO-1 also showed the same tendency (α-SMA: P=0.038; ZO-1: P=0.008). IL-13 significantly reduced the level of TNF-α (44.70±1.67 vs 31.79±3.53 pg/mL; P=0.005) at 48h, but the level of TGF-β2 was significantly increased from 34.44±2.92 to 57.61±6.31 pg/mL at 24h (P=0.004) and from 61.26±1.11 to 86.91±3.59 pg/mL at 48h (P<0.001). While expressions of VEGF didn’t change after IL-13 treatment. CONCLUSION: IL-13 in vitro inhibit ARPE-19 cell proliferation and expression in the aqueous may be associated with AMD.