Relationship between gas permeability and grain size of submerged arc welding (SAW) fluxes has been investigated to get information for the analysis of SAW process. SiO2-CaO-MgO glassy flux and SiO2-MnO porous flux were examined using a flux bed (50-mm-diameter and 50-mm-height) and nitrogen current to obtain the permeability by the D'Arcys' law.Firstly, an experimental equation which shows the relationship between the permeability and grain size was derived for the fluxes with a series of grain sizes ranging from 8×12 to 200×325 mesh. Secondly, it was shown that almost the same permeability as given by the above equation could be estimated for the glassy flux by changing the friction coefficient in the equation proposed previously by Shirai. Furthermore, the permeability of the above glassy flux with two-or four-grain size components was studied. By using the mean grain size obtained by considering the Kozeny-Carman condition, the estimation of permeability for these systems became possible with fair accuracy.