We investigated the effect of amino acids on changes in the particle shape and crystal form of tranilast within spray-dried particles (SDPs). Amino acid addition into an ethanol aqueous solution containing tranilast triggered the change in pH. Different amino acids affected tranilast formation in solution before spray drying. Consequently, the particle morphology of spray-dried tranilast changed. We investigated the crystal form of tranilast in SDPs using powder X-ray diffraction (PXRD) and fluorescence spectroscopy. PXRD pattern of tranilast SDPs with histidine was a typical broad amorphous band. Tranilast SDPs with leucine had a characteristic leucine crystalline peak, while the PXRD pattern of tranilast SDPs with aspartic acid had characteristic crystalline peaks associated with a stable crystal form of tranilast. On performing fluorescence analysis, the crystal form of tranilast with aspartic acid showed little or no change. The emission spectrum of tranilast in SDPs with histidine or leucine showed a blue shift compared with that of untreated tranilast crystals, indicating that histidine or leucine may induce the crystal transition of tranilast. Difference in crystal form of tranilast depending on amino acid species was strongly related to the effects of amino acids on tranilast nucleation and crystal growth. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.