To study the microstructural influence of dry or wet dentin bonding surface on the dentin bonding interface, five wet bonding systems were used to bond Chrisma B20 resin with dry or moist dentin surface with scanning electron microscope. All these systems were found to be well able to infiltrate into the dentin bonding interface on wet dentin surface, and significant changes occurred in the bonding interface when acetone-based adhesives were applied on dry dentin surfaces, demonstrating thinner hybrid layer and the formation of partially hybrid region, while alcohol- and water-based adhesives showed no changes. The necessity of moist dentin surface is therefore suggested when wet bonding systems are used.