Crystalline silica can devitrify with the formation of cristobalite and other crystalline silica species when exposed to prolonged high temperatures, which is of potential concern because crystalline silica is classified as carcinogenic. Silica particles activate macrophages to release oxidants, which contribute to inflammation and injury in the lower respiratory tract. Our aim was to compare silica particles with heat-treated silica particles for their ability to induce superoxide release from rat alveolar macrophages. We estimated the ability of four types of silica particle samples and heat-treated silica particles with different number average particle diameter to induce lucigenin-dependent chemiluminescence (CL) from macrophages based on the number of silica particles. A strong positive correlation was observed between particle diameter and the ability to induce CL in both the silica and heat-treated silica samples. Moreover, the ability of heat-treated silica samples to induce CL was approximately 43% of that of the silica samples. These results suggest that heat-treated silica reduces superoxide release from macrophages, and that the heat-treated reduces the biological effects of silica.