The degradation behavior of silicone rubber treated with ozone in water has been investigated. The materials used were commercially available silicone rubber containing polydimethylsiloxane (PDMS) and silica. As-received silicone rubber was cross-linked by peroxide. By the ozone-water treatments, the translucent sample changed into opaque one, the soluble fraction in the cross-linked sample for the degree of swelling decreased in the good solvent for PDMS. Chemical structure of the sample after ozone treatment for both soluble and insoluble parts of the samples in the good solvent for PDMS were evaluated by solid-state nuclear magnetic resonance (NMR) method, size exclusion chromatography, and gas chromatography - mass spectrometry. In addition, information on the interactions between PDMS and silica was obtained by ²⁹Si cross polarization / magic angle spinning NMR method, while might influence on the changes of degree of swelling of the sample by the ozone-water treatments.