In order to evaluate the thickness of the hybrid layer and depth of demineralization of dentin surfaces submitted to different treatments, dentin slices from human teeth were divided into two groups: one polished with 60-grit SiC paper and the other with 600-grit SiC paper. The adhesive systems applied were: Adhe SE®, Clearfil SE™ Bond, G Bond™ and Adper Single Bond™. After treatment, the samples were fractured and prepared and the smear layer, the effect of conditioners, and thickness of the hybrid layer were analyzed by SEM. The adhesive system and smear layer influenced thickness of the hybrid layer. The conditioners were more efficient over thin smear layer. A direct correlation was demonstrated between depth of demineralization and thickness of the hybrid layer. The smear layer was able to influence the depth of demineralization and thickness of the hybrid layer; however, for the total-etching adhesive system, thickness of the hybrid layer was independent of the smear layer.