A stability study and thermal behavior of thiabendazole pre-formulation and tablets were investigated by TG and DSC coupled to a photovisual system. The results showed that the excipients, namely starch, PVP and magnesium stearate did not cause significant chemical interactions with the drug thiabendazole. The rate constants for the thermal decomposition reaction were determined by both an isothermal thermogravimetry and oven accelerated decomposition methods using the classical Arrhenius' equations. Thermal stability studies showed that thiabendazole tablets presented lower stability than the drug thiabendazole. The data analysis revealed that the drug thiabendazole undergoes a thermal decomposition reaction at a temperature lower that its melting point. This fact was confirmed by DSC coupled to the photovisual system and FT-IR.