Abstract: Tadalafil (TD), a phosphodiesterase-5 inhibitor for the treatment of erectile dysfunction, has a low oral bioavailability due to its extremely poorly aqueous solubility. The aim of this study was to enhance its solubility and dissolution by coamorphization with dapoxetine (DP), a selective serotonin reuptake inhibitor to manage premature ejaculation. Coamorphous TD-DP (molar ratio, 1:1) was prepared by solvent-evaporation method and characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR). The supersaturated dissolution of TD from coamorphous TD-DP was investigated in various aqueous media and compared to that of crystalline TD. In addition, physical stability of coamorphous system was also evaluated under the conditions of 40℃/75% relative humidity (RH) and 25℃/60% RH for 90 days. DSC thermogram and PXRD pattern indicated the formation of the coamorphous TD-DP. In comparison to original TD crystal, the dissolution of TD from coamorphous system were significantly enhanced in various media (water, 0.01 mol·L^-1 HCl and pH 4.5 phosphate buffer). In addition, no crystallization phenomenon of the prepared coamorphous system was observed until 90 days' storage under 25℃/60% RH. However, when temperature and humidity were increased to 40℃/75% RH, the coamorphous TD-DP was recrystallized easily.