Purpose: To evaluate the MMP-inhibitory effect of chlorhexidine when incorporated in the primer of a two-step selfetching adhesive (Clearfil SE Bond). Materials and Methods: Powdered dentin made from human teeth was treated with Clearfil SE Bond primers containing chlorhexidine of different concentrations for 20 s or for 2 min. The collagenolytic activity of the dentin powder was assayed using fluorescein-labelled collagen. Results: Untreated dentin powder contains a low but measurable level of intrinsic activity, which was significantly inhibited by 0.05% chlorhexidine. Treating dentin powder for 20 s with SE Bond primers containing chlorhexidine (0.5%, 1.0%, and 2.0%) reduced the collagenolytic activities by 15.6%, 44.9%, and 56.7% respectively. When treated for 2 min, only SE Bond primer containing 2.0% chlorhexidine could inhibit the collagenolytic activity by 41.1%. Conclusion: When incorporated in a two-step self-etching adhesive primer (Clearfil SE Bond primer), chlorhexidine can partially maintain its inhibitory effect on MMPs. Keywords: chlorhexidine, matrix metalloproteinases, self-etching adhesives, bond degradation, collagenolytic activity