A hydrogel kept at its equilibrium swelling state during taking the measurements controlled in a diffusion cell. The diffusion data gained from Raman spectra were analyzed to calculate the mutual diffusion coefficient in the hydrogel as semi-infinite medium. The relation between the solute concentration and Raman intensity for poly(N-isopropylacrylamide), which is characterized by the distinct peak for the isopropyl group at 2925 cm-1 was taken into account. The determination of the mutual diffusion coefficient, Dmut for hydrogels/phenol system was achieved successfully using confocal Raman spectroscopy at different solute concentrations. At 25oC, the value of the mutual diffusion coefficient is found between 5.61845x10-11 m2/s and 3.34565x10-9 m2/s for the hydrogel loaded with phenol of an initial concentration of 0.01 mM and 0.1 mM, respectively.