Abstract: Due to the unique ionization properties of microwave plasma, it can be used as an ion source for atmospheric pressure mass spectrometry, both for the analysis of organic small molecules and the detection of inorganic metallic elements. To improve the performance of microwave plasma ionization sources for the analysis of metallic elements in aqueous solutions, the mass spectrometric behaviour of manganese (Mn) in kilowattmicrowave plasma mass spectrometry (KMP-MS) with a novel injection system (NafionH2SO4) was investigated. The KMPMS characteristic spectra of Mn had new features that were significantly different from the characteristic signals obtained by traditional inductively coupled plasma (ICP-MS), which might be useful for the detection of metal elements. The complex anions of Mn in water were analyzed using the KMPLTQMS, confirming that these complex anions were produced by aqueous solutions flowing through the KMP central tube in a plasma flame, such as NO3-. In addition, the form of the major ions was explained during multi-step collisioninduced dissociation. The limit of detection (LOD) of Mn was 0.33 μg/L under the optimized conditions using its secondary mass spectrometric characteristic ions, while the linear dynamic range covered at least two orders of magnitude (0100 μg/L). This method is suitable for analysis of metal elements in water and Mn ions in real samples. Because there is no Ar background interference in KMP source, the combination of the KMP source and quadrupole mass spectrometry will provide a new powerful analytical tool for multielement detection in areas, such as environmental pollution, criminal investigation, and geological exploration.