Objective：To establish a method for the determination of magnesium oxide (MgO) in serpentine.Method:HCl is used to dissolution the sample directly.In the ammoniacal buffer solution that pH is 100，triethanolamine、potassium sodium tartrate and sodium diethyldithiocarbamate are used to cover interference ions.MgO is determined by EDTA titrametic method with the K-B indicator.Results:The calibration curve is linear in the range of 3357mg～10071mg for magnesium ion,the regression equation being V=0.824 5×m-0.108 3，r=0.999 9（n=5）,and the average recovery was 1000% with RSD 23%.Conclusion:The end point is changing obviously and the method is simple,accurate and reproducible for quality control of serpentine.