Abstract: The aim of this study was to compare the physicochemical properties and in vivo behavior of two crystal forms of iguratimod. The different crystal forms of iguratimod were prepared and their physicochemical properties were studied by DSC and XRPD. The absorptions of the crystal forms α and β was compared by administering iguratimod to SD rats. It was found that the melting points and solubilities, as well as pharmacokinetic parameters of crystal forms α and β were similar. No significant difference was found in biological activity in the rats between them. Meanwhile, the flowability and compressibility of crystal form β were better than those for form α. Therefore, the crystal form β is more suitable for the development of solid formulation.