Objective To investigate the effect of arsenic trioxide (As2O3) on the metastasis capability of Ewing's sarcoma ceils. Methods MTT assays were performed to choose appropriate concentrations of As2O3 (＜ 2 μmol/L) for the experiments.Migration and invasion assays were performed to assess the effect of As2O3 on the metastasis of Ewing's sarcoma cells. Changes in matrix metalloproteinase (MMP)-9 expressions were detected by gel zymography assay and the phosphoinositide 3-kinase/AKT (PI3K-AKT) pathway was investigated using Western blot. Results The amount of Ewing's sarcoma cells across basal membrane of Transwell in migration and invasion assay decreased gradually with the increase in As2O3 concentration. The average quantities of A-673 across the membrane after treatment by gradual concentrations accounted for 54.3 ％,49.0 ％ and 17.0 ％ of that of untreated group respectively in migration assay (F=112.78,P ＜ 0.01), while 52.7 ％, 32.3 ％ and 10.3 ％ in invasion assay (F =183.76, P ＜ 0.01). Similarly, the percentage of RD-ES was 46.0 ％,39.0 ％ and 8.0 ％ in migration assay (F =408.25,P ＜ 0.01) and 58.7 ％,22.3 ％ and 9.0 ％ in invasion assay (F =373.25, P ＜ 0.01) respectively. The difference had statistics significance.The expression of MMP-9 was suppressed by As2O3 treatment according to gel zymography assay.Western blot assay showed that PI3K-AKT pathway was inhibited and nuclear factor kappa B (NF-κB) was inactivated.Conclusion Low-concentration As2O3 may inhibit metastasis capability of Ewing's sarcoma cells.