Abstract: Due to its water-solubility and different half-life, Ra isotopes play important roles in biogeochemical process, water exchange and groundwater movement in estuaries and marine coastal areas. The efficiency of Mn fiber application is an important factor for the determination of Ra isotopes in seawater. In this study, the Mn fiber was made by KMnO₄ solution and polypropylene fiber. The detailed parameters of Mn fiber manufacture are optimized and the experimental results are analyzed by scanning electronic microscope. The effect of the Mn fiber manufacture can be evaluated by the surface morphology under the scanning electronic microscope and the elemental analysis using energy spectrum. So scanning electron microscope could be an effective tool for assessment of Mn fiber manufacture.