Mass transfer characteristics of gas diffusion layer (GDL) are closely related to cell performance in polymer electrolyte fuel cell (PEFC). The four types of GDLs (Paper, Cloth, New structure with hydrophilic and hydrophobic layers and paper with MPL) were evaluated as specimens. The images of liquid water distribution in the GDLs were taken by neutron radiography. The images led to a further understanding of relation between the specifications and liquid water distribution. Simulaneous measurement of oxygen diffusivity characteristics was conducted in parallel. The experimental results led to a further understanding of relation between the liquid water distribution and oxygen diffusivity characteristics. It is clarified that the methods of visualization by neutron radiography and simultaneous measurement of oxygen diffusivity characteristics by an experimental appatatus consisting of oxygen sensor based on Galvanic battery can be used to evaluate the effect of GDL specification to liquid water distribution and the resultant oxygen diffusivity characteristics as effective tools. These elucidate the relations and its mechanisms. The following findings are revealed ; The specification of GDL greatly influences its water distribution under the experimental condition of evaporation from one edge face, The findings on liquid water distribution increases the understanding of oxygen diffusivity characteristics.