A silver chelate of 2-(4-thiazolyl)-benzimidazole, dodecyltrimethylammonium cation and hexadecylpyridinium cation have been intercalated between montmorillonite, and the resulting samples were subjected to examination of their thermostabilities by thermogravimetry and carbon dioxide evolution analysis up to 500 degrees C in air. The degradation behaviour of the intercalant was significantly changed by intercalating between the montmorillonite layers. Two quaternary ammonium cations were released from the montmorillonite both at the same temperature, which was higher than those for the quaternary ammonium cations themselves. This relation was also observed in the case of 2-(4-thiazolyl)-benzimidazole. The improvement of the thermostability after intercalation can be attributed to the bonding between the intercalant and the host montmorillonite layers.