The leaching behavior of Na from soda-lime-silicate glass was investigated by preparing glass powders with average particle diameters of 53 and 19 mu m, and leaching in HNO3 at 90 degrees-140 degrees C. A new theoretical equation for Na leaching from a spherical particle is proposed based on the assumption that a rate-determining process is the three-dimensional self-diffusion of Na in glass. The diffusion constant (D) of Na in glass was obtained by fitting the experimental data to a theoretical equation. The values of D and activation energy obtained are comparable to those obtained in other studies on larger particles.