The present study was directed to evaluate the effect of fluoride Iontophoresis application on microleakage of low shrinkage resin composites. Materials and Methods; A total of 180 freshly extracted human non carious premolar teeth were used. Three (C- factor) (60 teeth each), half of the teeth received fluoride Iontophoresis application (FI), while the other half were not received any treatment (NF). Teeth were restored with Silorane resin composite and Kalore resin composite. The specimens stored for one month, three months and six months in distilled water at 37^o C in an incubator. After storage time and sealing procedures and dye immersion in silver nitrate 50% wt. for 12 hours. The tooth restoration interface and investigated under Scanning Electron Microscope (SEM). Result; The results of this study revealed that less microleakage of Silorane than kalore. There was significant difference between flat tooth surface and both of classII and classV. Lower leakage score for the fluoridated Silorane and kalore restorations than none fluoridated one at all C-factors and at three and six storage times. Conclusions; Fluoride iontophoresis have a better effect on microleakage. C-factor significantly affected on the marginal seal.