Sulfamethoxazole and trimethoprim (SMX/TMP) tablets are generally large in size because they contain 400 mg SMX and 80 mg TMP. The large size of tablets negatively affects patient adherence, especially among pediatrics. In this study, SMX/TMP tablets were prepared at an approximately quarter of the weight of conventional tablets (6 mm diameter, and varying thicknesses), and their physical properties were compared. Tablets with thicknesses of 3.80-4.60 mm met the criteria for friability and disintegration time and showed no weight variation even though the mass was reduced to a quarter of the conventional formulation. Moreover, the dissolution profiles of the tablets with 4.26-4.51 mm thickness were equivalent to those of conventional tablets. Using these results, we successfully formulated and launched mini SMX/TMP tablets in December 2021 in Japan. We report the details of various comparative evaluation in order to develop mini SMX/TMP tablets as a case study of drug product development.