The purpose of this study was to evaluate the ability of seven dentin bonding agents to reduce dye penetration at the margins of microfill composite restorations in dentinal cavities.Forty extracted molars were selected and cleaned. Cavity preparations were made in dentin with #55 carbide burs. The preparations were restored with Silux after application of one of the following dentin bonding agents: Gluma, Scotchbond 2, Tenure, Prisma Universal Bond 2, Mirage‐Bond, XR Bond, and All‐Bond. Samples were thermocycled for 200 cycles between 3°C and 60CC, then immersed in a 0.05 percent crystal violet solution for 2 hours. The samples were embedded in clear casting resin, sectioned, and examined with a light microscope.Our results indicated that the dentin bonding systems reduced, but failed to totally eliminate, microleakage around the composite resin restorations.