In situ UV/Vis spectroscopy was used to study supercritical fluid impregnation of azo-dyes with varying functional groups into poly(methyl methacrylate) (PMMA) films. The diffusion and phase behavior of Disperse Orange 25 (DO25) and a dye mixture of Disperse Red 1 and DO25 in PMMA/CO 2 system were studied. Although these azo-dyes are relatively insoluble in supercritical carbon dioxide (scCO 2 ) (<10 - 6 M under conditions of our experiments), the high partition coefficients (~10 4 -10 5 ) between PMMA and scCO 2 phase allow incorporation of ~1% of these dyes into PMMA matrix. The diffusion of azo-dyes in scCO 2 -swollen PMMA film was observed in situ via UV/Vis spectroscopy, and can be tuned simply by changing the CO 2 pressure surrounding the polymer film. This article reports the effects of CO 2 pressures and specific intermolecular interactions on the diffusion rate (or diffusivity) and the partitioning of dye solutes between the fluid phase and the PMMA. It also demonstrates a possibility of enhancing diffusion by a dye mixture that is capable of mutual intermolecular interactions and thus reducing interactions with the polymer matrix.