Abstract: Application of MAT-251 Mass Spectrometer to ~(13)CO_2-Breath TestWen Qibing(Lanzhou Institute of Geology,Chinese Academy ofSciences,Lanzhou 73000,China)Zheng Wenbing(Lanzhou Institute of Modern Physics,Chinese Academy ofSciences,Lanzhou 730000,China )Received Abstract:The construction and the characterstics as well as the measuring method of MAT251 mass spectrometer are briefly described.The application of this instrument to the 13CO2-breath test is reported.Keywords:~(13)CO_2-breath test;stable isotope mass spectrometer;abundance sensitivity;δ~(13)C