This study aimed to select an appropriate active pharmaceutical ingredient (API) manufacturer for the development of a novel tyrosine kinase inhibitor (TKI) tablet by comparing the solubility and dissolution characteristics of two TKIs with different particle sizes. Dynamic light scattering (DLS) analysis revealed that TKI (a) had a particle size of 4 µm, whereas TKI (b) had a particle size of 24 µm. Equilibrium solubility tests showed that both TKIs had similar solubility values of 0.5 mg/mL in pH1.2 solution. However, in pH4.0 solution, TKI (a) exhibited a solubility of 0.4 mg/mL, while TKI (b) had a solubility of 0.18 mg/mL. This difference is presumed to be attributed to the difference in API particle size. To assess the bioequivalence of tablets manufactured using the two TKIs, comparative dissolution tests were conducted in pH1.2, pH4.0, and pH4.5 solutions. The results indicated that both formulations exhibited similar dissolution profiles to the reference drug in pH1.2 solution. However, in pH4.0 solution, the tablet formulated with TKI (a) was more similar to the reference drug, whereas in pH 4.5 solution, the tablet formulated with TKI (b) exhibited a dissolution profile more comparable to that of the reference drug. This study demonstrates the impact of API particle size and solubility on the dissolution profile of the final drug product. These findings are expected to aid in developing high-quality oral solid dosage forms through optimized API selection.