The particle size distribution of floating spherical solid particles was measured using the buoyancy weighing-bar method. Systems of soda lime silicate glass beads (JIS Test Powders 2, GBL100) in sodium polytungstate solution and hollow glass beads (Glassbubbles K1, S60HS) in water were experimentally investigated. The particle size distribution obtained in our experiments agreed with the particle size measured by laser scattering/diffraction and by microscopic observation. The present study demonstrates that the buoyancy weighing-bar method is suitable for measuring the particle size distribution of floating spherical solids. The precision of the resulting particle size distribution is comparable to that of the laser diffraction/scattering method as well as a direct measurement under the microscope.