Decomposition of crystalline potassium nitrate due to He+-, Ar+-, and Xe+- ion bombardment was studied in the energy range from 20 to 100keV. The cross sections for producing nitrite ions were for the first time determined to be 5.7×10−20m2, 12.6×10−20, and 22.0×10−20m2 for 100keV He+, Ar+, and Xe+ ion, respectively. Comparing the values of these cross sections with the rate of an elastic and inelastic energy loss of these incident ions, which were calculated on the basis of the theory of Lindhard et al., it may be concluded that inelastic energy is about five times more efficient than elastic energy for the decomposition of the solid potassium nitrate.