The molecular states of ketoprofen and the interaction between ketoprofen and other pharmaceutical excipients in the matrix layer were examined to determine their effect on the pharmaceutical properties of original and generic ketoprofen dermal patches (generic patches A and B). Molecular states of ketoprofen were evaluated using polarized light microscopy, Raman spectroscopy and powder X-ray diffraction. For the original ketoprofen patch, crystalline components were not observed in the matrix layer. However, crystalline ketoprofen was observed in the two generic ketoprofen patches. Moreover, the ketoprofen exhibited hydrogen bonding with the pharmaceutical excipients or patch materials in the generic products. Skin permeation of ketoprofen from the patches was evaluated using hairless mouse skin. Twelve hours after application, the original patch demonstrated the highest level of cumulative skin permeation of ketoprofen. This was followed by generic patch B while generic patch A showed the lowest level of permeation. Fluxes were calculated from the skin permeation profiles. The original patch was approx. 2.4-times faster compared with generic patch A and approximately 1.9-times faster compared with generic patch B. This investigation suggested that pharmaceutical properties such as skin permeability for these types of products are affected by the precipitation of crystalline ketoprofen in the matrix layer and the interaction of ketoprofen with the pharmaceutical excipients or patch materials.