The solubility of salicylic acid in three mixtures of polyethylene glycol (PEG) with different molar masses of 200 to 600 g/mole were experimentally determined by a shake flask method at temperature range of (293.15 to 313.15) K under ambient pressure (≈85 kPa). The experimental results indicated that the solubility of salicylic acid enhanced by the introduction of PEGs to the water, and that could be explained with Hansen’s parameters and like-dissolves-like rule. Based on the results, PEG 600 had the best solubilization power, whereas PEG 200 displayed the lowest solubilization power, and generally the solubility decreased with decreasing molar mass of PEG and also decreasing temperature. Moreover, the equilibrium solid phase crystal of salicylic acid is characterized with X-ray powder diffraction analysis to identify no polymorphic transformation, solvate formation or crystal transition during the whole solvent crystallization process. A number of linear and nonlinear cosolvency models including the Jouyban-Acree based models along with the equations of van’t Hoff, the mixture response surface, the combined nearly ideal binary solvent/Redlich-Kister, λh and the modified Wilson-van’t Hoff were challenged to correlate/predict the solubility of salicylic acid in these mixtures. The computed values of the Jouyban-Acree based models presented a good agreement with the experiment data than the others, as a consequent of a low mean percentage deviation (MPD ≤ 15.7%). According to the enthalpy–entropy compensation analysis, there observed slope changes indicating that two mechanisms, enthalpy or entropy controlled the solubility increment depending on the PEG mass fraction in each solution.