Abstract: The oxide interference for The determination of rare each elements (REEs) at sub ng/g levels in human hair and wheat flour reference materials by inductively coupled plasma mass spectrometry(ICP-MS) is described. The linear regression indicated that The contribution of BaO at 0.1 to 0.7 u g/ml levels on ~(151)En and 153Eu peaks is a linear correlation. The correlation coefficients are 0.99863 and 0.99945, respectively. Analyzing a solution containing only Ba and calculating the percentage contribution of BaO to Eu peak made a correction for BaO interferences. The efficiency of The maThematical correction method was validated by analyzing a range of different levels of Ba on The same or different levels of Eu. The recoveries after oxide interference correction are within an acceptable range. The interference from The formation of LREE oxide is also a serious practical problem. The use of two standard calibration solutions (LREE and HREE are separated) is recommended.