Objective To study the function of interleukin (IL)-25 for rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) differentiation as well as on the expression of extracellular regulating protein kinase (ERK) and matrix metalloproteinases-3 (MMP-3).Methods The differences on ERK1/2 and MMP-3 protein levels were tested in RA-FLS of RA patients and healthy controls,then IL-17A (10 ng/ml) was tested when the RA-FLS were co-stimulated with different concentrations of IL-25 (0.01,0.1,1 and 10 ng/ml) and IL-17A(10 ng/ml) for 24 hours respectively.The expression of ERK1/2 and MMP-3 protein was detected by the Western blot.T test was used for the comparison between different groups.Results The expression of ERK1/2 (1.71±0.17) and MMP-3 (0.50±0.13) proteins in RA-FLS was higher than the healthy controls (0.50±0.15,0.17±0.05) (t=-9.13,P＜0.01 and t=-4.10,P＜0.05),after stimulated with IL-17A,the expression of ERK1/2 (0.77±0.22) and MMP-3 (0.59±0.13) proteins in RA-FLS were increased compared with the untreated groups (0.18±0.35,0.04±0.03) (t=-4.69,P＜0.01 and t=-7.47,P＜0.01).With increase of the concentration on IL-25,the level of ERK1/2 (0.54±0.26,0.48±0.18,0.48±0.23,0.23±0.06) and MMP-3 (0.58±0.09,0.59±0.14,0.21±0.04,0.04±0.02) in RA-FLS which were stimulated by IL-17A was decreased slowly (t=4.22,P＜0.05 and t=4.95,P＜0.01 and t=7.47,P＜0.01).Conclusion IL-25 can inhibit the stimulation of IL-17A on ERK1/2 and MMP-3 fractionally,which implies that it may take part in the development of RA through this pathway and may be a target for the RA treatment.