In present study, the solubility data of tadalafil in mono-solvents and various polyethylene glycol 400 (PEG 400) + water co-solvent mixtures from 298.15 to 333.15 K was measured. The experimental mole fraction solubility data of TDL from 298.15 to 333.15 K was measured and correlated. The experimental solubilities of TDL were regressed by the modified Apelblat model with absolute relative deviation in the range of 0.0006-2.2000 % in all co-solvent mixtures. However, the correlation coefficients were observed in the range of 0.9955-0.9998. The mean absolute errors by Yalkowsky model were observed in the range of 0.332-0.442. The mole fraction solubility of TDL was found to be highest in pure PEG 400 (1.86 × 10- 2 at 298.15 K) as compared to water (5.7 × 10- 7 at 298.15 K). The thermophysical parameters such as enthalpies and entropies for TDL dissolution indicated that the dissolution of TDL is endothermic and an entropy-driven process.