Stainless steel non-woven fiber filters with various of fiber diameters, basis weight and porosity were used to examine the effects of these variables on filtration characteristics and pore size distribution. The average pore size measured by the liquid permeation method was proportional to the fiber diameter and increased with the increase in porosity, but was independent of the basis weight change. The maximum pore size measured by the bubble point test increased as the porosity increased, and it decreased as the basis weight increased at the same porosity. The fiber distance distribution measured by microscope observation corresponded to a gamma distribution. The relationship between average fiber distance calculated from the gamma distribution and porosity agreed closely with the relationship between average pore size and porosity. Maximum particle size measured by the particle challenge test with latex beads, namely the size of particles of which 99% are blocked by the filter, increased as the porosity increased, but gradually decreased as the basis weight increased.