A versatile method is presented for the preparation of porous inorganic hollow fibers with small tunable radial dimensions, down to ∼250 μm outer diameter. The approach allows fabrication of thin hollow fibers of various materials, as is demonstrated for alumina, nickel, silicon carbide, stainless steel, and yttria stabilized zirconia. The preparation method is based on dry-wet spinning of a particle-loaded polymer solution followed by thermal treatment. Exceptionally small radial dimensions have been achieved by surface energy driven viscous flow of the green fiber, resulting in a reduction of macro-void volume. It is shown that the extent of viscous deformation is directly related to the rheology of the particle-loaded green fiber above the glass transition temperature of the polymer. A particle specific limited concentration range can be identified in which viscous deformation is possible. Above a critical particle volume fraction the viscosity of the particle–polymer material increases sharply and the time scale of viscous deformation becomes too long. Below a minimum concentration of particles it is not possible to sinter the particles together. For small particles of alumina, silicon carbide, and yttria stabilized zirconia the concentration range allowing viscous deformation is very narrow as compared to that of larger metal particles.