Objective:To study the cytocompatibility of Zr-Cu-Al-Ag alloy coated by micro-arc oxidation.Methods:Components of Zr-Cu-Al-Ag alloy coated by micro-arc oxidation in three different voltages of 300 V,350 V and 400 V,Zr-Cu-Al-Ag alloy as cast condition and TI6Al4V alloy were made for the test.The water extracted from the components were obtained according to national standard.The L929 cells were cultivated in vitro in the extracts of these components separately.The L929 cells,cultured in Dulbecco's modified Eagle medium supplemented with 10 ％ fetal calf serum,served as the negative control group.And cells,cultured in Dulbecco's modified Eagle medium supplemented with 10 ％ fetal calf serum and 64 g/L phenol,served as the positive control group.The cytocompatibility of these components were evaluated by MTT colorimetric.Results:The cytotoxicity of Zr-Cu-Al-Ag alloy coated by micro-arc oxidation is 0 grade.Microscopy showed that the morphology of L929 cells,cultured in the extracts of Zr-Cu-Al-Ag alloy coated by micro-arc oxidation were normal.There were no significant differences between micro-arc oxidationt and negative control groups.The cell multiplication curves of micro-arc oxidation and negative control groups were nearly overlapping and in the linearity increasing trend.The OD in micro-arc oxidation groups had no significant differences with negative control group (P＞0.05),but were higher than that of Zr-Cu-Al-Ag alloy as cast condition,TI6Al4V alloy and positive control groups (P＜0.05).Conclusions:The cytocompatibility of Zr-Cu-Al-Ag alloy has been improved by micro-arc oxidation technique.