The aim of the present study is to investigate the effect of PH of storage medium on volumetric changes and tooth restoration interface of a silorane based resin composite and a nano-hybrid resin composite at different time periods. For volumetric dimensional changes, a total of sixty specimens was prepared by applying each restorative material [a silorane based resin composite (Filtek P90) and a nano-hybrid resin composite (Filtek Supreme XT) ] inside a central hole of 2mm diameter and 3mm height of standardized teflon mold and cured following manufacturer instructions. Length and diameter of each specimen was measured before and after storage using a digital caliper, change in volume was then calculated using mathematical equation. For tooth restoration interface evaluation, a standardized class V cavities were prepared on buccal surface of sixty premolars which were then restored with resin composites according to manufacturer instructions. The prepared specimens were longitudinally sectioned bucco-lingually then a stereomicrograph was captured by a digital camera mounted on a Zoom Stereomicroscope before and after storage. Gap width and surface area was measured using a special image analysis software.The results showed no statistically significant difference was found between volumetric dimensional changes of Filtek P90 and FiltekSupreme XT initially. However, after 3 months Filtek P90 showed higher contraction than Filtek Supreme XT. Results of tooth/restoration interface revealed that Filtek P90 showed higher mean gap dimensions than Filtek Supreme XT through all periods however the differences were statistically significant in neutral media but non-significant in acidic.Conclusion: Silorane based resin composite undergoes volumetric dimensional changes comparable to nanohybrid resin composite except on long term storage where it revealed overall contraction at different PH of storage media. Gap dimensions at tooth/restoration interface of silorane based resin composite was worse compared to that of nanohybrid resin composite at different PH media at different periods of time.