Abstract： Fine γ-Fe2O3 particles with diameter of 80-700? were prepared. Their saturation magnetization per unit mass σs and specific surface area Sa were measured. An empirical formula σs(s) = σs(∞(1-aSa) was obtained. It was proposed that the fine particles consist of two parts: the first part is the surface layer, whose magnetic moment can not be turned entirely to the field direction by the applied magnetic field, but make an average angle (canting angle) with the field. The second is the inner part of the particles, whose magnetic moment can be aligned along the direction of the applied magnetic field. The above empirical formula can be interpreted very well by this simple model.