AIM: Age-related macular degeneration (AMD) is a multifactorial disease and a prevalent cause of visual impairment in developed countries. Many studies suggest that age-related maculopathy susceptibility 2 (ARMS2) is a second major susceptibility gene for AMD. At present, there is no functional information on this gene. Therefore, the purpose of the present study was to detect the expression of ARMS2 in retinal pigment epithelium (RPE) cells and to investigate the effect of ARMS2 on the phagocytosis function of RPE cells. METHODS: Immunofluorescence and reverse transcriptase PCR were used to demonstrate the presence and location of ARMS2 in ARPE-19 (human retinal pigment epithelial cell line, ATCC, catalog No.CRL-2302) cells. siRNA was used to knock down ARMS2 mRNA, and the effects of the knockdown on the phagocytosis function of the ARPE-19 cells were evaluated via Fluorescence Activated Cell Sorting (FACS). RESULTS: ARMS2 was present in ARPE-19 cells, localized in the cytosol of the perinuclear region. The expression of ARMS2 mRNA (messenger RNA) in ARPE-19 cells transfected with ARMS2-siRNA (small interfering RNA, 0.73±0.08) was decreased compared with normal cells (1.00±0.00) or with cells transfected with scrambled siRNA (0.95±0.13) (P＜0.05). After incubation of RPE cells with a latex beads medium for 12, 18, or 24 hours, the fluorescence intensities were 38.04±1.02, 68.92±0.92, and 78.00±0.12 in the ARMS2-siRNA-transfected groups, respectively, and 77.98±5.43, 94.87±0.60, and 98.30±0.11 in the scrambled siRNA-transfected groups, respectively. The fluorescent intensities of the same time points in the two groups were compared using Student’s t-test, and the p values were all less than 0.001 at the three different time points. CONCLUSION: There is endogenous expression of ARMS2 in ARPE-19 cells. ARMS2 plays a role in the phagocytosis function of RPE cells, and this role may be one of the mechanisms that participates in the development of AMD.