OBJECTIVE： To compare the difference in the concentration determination of valproic acid （VPA） in human serum by LC-MS/MS and EMIT. METHODS： Both LC-MS/MS and EMIT methods were applied to determine the serum concentration of VPA in 144 inpatients or outpatients. The paired t-test， Pearson correlation analysis， Bland-Altman deviation chart and other methods were used to evaluate the difference in the results of concentration determination. RESULTS： The results of LC-MS/MS method was positively correlated with that of EMIT method （r＝0.924，P＜0.05）； the regression equation of them was cEMIT＝0.920 7cLC-MS/MS-1.114 4（r＝0.924）. Average serum concentrations of VPA determined by LC-MS/MS and EMIT were （49.9±21.2） and （54.9±21.3） μg/mL， with statistical significance （P＜0.05）. The serum concentration of VPA determined by EMIT was higher than that by LC-MS/MS 8.3 μg/mL， 95％ confidence interval was （－13.6，18.7）. CONCLUSIONS： The serum concentration of VPA determined by LC-MS/MS and EMIT have high correlation. But the determination results still have certain difference， it is suggested to use same method for long- term monitering.