-Semi interpenetrating networks (IPNs) of the Silicone epoxy resin and poly (methyl methacrylate) (PMMA) were prepared by the sequential mode of synthesis. These were characterized with respect to their mechanical properties, namely, tensile strength, elongation at break. Thermal properties were studied by differential scanning calorimetry, thermogravimetry and dynamic mechanical thermal analysis. The morphological features were studied through scanning electron microscopy(SEM). The effects of variation of the blend ratios between silicone epoxy and poly(methyl methacrylate) on the above-mentioned properties were examined. There was a gradual increase of tensile strength with consequent increases in elongation at break for both types of IPNs with increases in PMMA content up to 30% and further the above properties were decreased with increasing PMMA. The weight retentions in the thermal decomposition of both the semi-IPNs and full IPNs were higher than the silicone epoxy system. This enhancement was would be related to the presence of the unzipped methyl methacrylate monomer, which acted as radical scavengers in the silicone epoxy degradation. An inward shift and lowering (with respect to pure epoxy) of the Tg of the IPNs was observed. The fractography as studied by SEM shows change in fracture mechanics from shear yielding to crazing with increasing PMMA content.