Introduction In our society, with the advances in cosmetic consciousness, well-aligned, properly contoured, white and clean teeth are a symbol of health and standard of beauty. Thus, tooth bleaching has become popular cosmetic therapy among patients and dentists. Microleakage is a major challenge to the success rate for all type of restorations. Materials and Methods Eighty maxillary human molars were collected and evaluated and Class V cavities 5×3×2 mm size were prepared with straight carbide bur (SS White) on the buccal and palatal surfaces at the cementoenamel junction of all the samples, so that the upper margin would be in enamel and lower margins on root surface. In total, 160 class V cavities were prepared on maxillary molars. Then samples were randomly divided into 3 groups (microfilled and nanohybrid composite resins and control group) and 3 subgroups (Pola Office, Whiteness HP Blue, Whiteness Perfect) according to the type of composite resins and bleaching agents used. After application of bleaching agents, all samples were immersed in a contrast solution of rhodamine B fluorescent dye for 24 hours. Then using a diamond disc samples were sectioned buccolingually through the center of the restorations and sectioned teeth were evaluated for marginal microleakage under confocal laser scanning microscope to check the extent of dye penetration. Results When all composite resin groups were compared with all the bleaching agents, at occlusal and gingival levels, lowest marginal leakage scores were obtained with the microfilled composite resin bleached with Whiteness HP blue, and in nanohybrid composite lowest microleakage score were obtained with Pola office bleach at both levels.