We evaluated the removal of polymers with various chemical structures using wet ozone, and investigated the reaction mechanism between wet ozone and polymers using fourier-transform infrared (FT-IR) and in situ FT-IR. The removal rate of poly(vinyl phenol) (PVP), which has a carbon–carbon double bond (C=C) in the side chain was lower than that of the novolak resin, which has C=C in the main chain. Poly(methyl methacrylate) (PMMA), which has no C=C, was not removed. It was considered that the ozone reaction is an electrophilic reaction, and the wet ozone should react with C=C with ease. The removal rate of PVP with rinsing was higher than that without rinsing. This result indicates that the reaction products remain on the Si wafer. However, in the novolak resin, there was no difference between with and without rinsing. It was considered that the main chain of the novolak resin was decomposed to gas by the reaction with wet ozone. In the FT-IR measurement of PVP, the peak intensity of C=O stretching of carboxylic acid increased with increasing wet ozone processing time. However, in the novolak resin, there was no difference between with and without rinsing. Moreover, the peak intensity of the C=O stretching of carboxylic acid did not increase with increasing wet ozone processing time after 10 s of wet ozone processing time. From the result of in situ FT-IR, in the removal of the novolak resin using wet ozone, the main chain of the novolak resin was decomposed, and the reaction products of the wet ozone and novolak resin (low-molecular-weight carboxylic acid) should change to CO2.