Abstract: The Expression of Measurement Uncertainty in Isotopic Standard Materials PreparationAuthor Yao Jijun,Zhang Hongjing,Li Jinying(China Institute of Atomic Energy,Beijing 102413,China)Received 19980929 Abstract The uncertainty expression formulae in isotopic standard reference materials preparation are given,and influences of factors such as the enrichment of raw materials,mass spectrometry measurement and the expected abundance of isotopic standard reference materials are discussed.The method is applied for an example.Key Words: isotopic standard reference materials,mass spectrometry measurement,uncertainty