Purpose To study inhibition effects of retinal pigment epithelial (RPE) cells by hyaluronic acid-stimulating activity(HASA)． Methods The cultured human RPE cells added with a series of HASA was measured with cell counting,tetrazolium(MTT)colorimetric assay and tritium labelled thymidine deoxyribosｅ(3H-TdR)incorporation assay.Flow cytometry(FCM)analysis was used to examine RPE cells cycles. Results HASA at concentrations of 12.5～200 mu;g/ml and within 48 hours inhibited RPE cells proliferation with a dose-dependant and time dependant manners.The maximal inhibition rate of RPE cells by HASF was about 48.0%.FCM revealed that the cells in G1 phase increased 7.2% and cells in S phase decreased 9.7%,compared to controls. Conclusion HASA at a certain dose range and period can inhibit RPE cells proliferation. (Chin J Ocul Fundus Dis,1999,15:72-74)