Purpose: To evaluate the effect of different dentin conditioning procedures for resin bonding on dentin surface properties (i.e., wettability, roughness and nano-hardness). Methods: Polished human dentin surfaces were obtained and treated with: (1) 35% phosphoric acid (15 s); (2) 0.1 M ethylenediaminetetreaacetic acid (EDTA) (pH 7.4) (60 s); (3) 35% phosphoric acid (15 s) followed by 3% potassium oxalate gel (120 s). Contact angles were measured with water, to assess the surface wettability and were done by axisymetric drop shape analysis; the average roughness (Ra) was measured using a contact profilometer and an atomic force microscope; and the nano-hardness was assessed using a Berkovich diamond tip mounted in a Hysitron triboscope nanoindenter. The conditioned surfaces were bonded with an etch and rinse adhesive system (Single Bond) and bond strength was assessed using a microtensile bond strength test. Data were examined by analysis of variance and Student-Newman-Keuls multiple comparison tests (p < 0.05). Results: All the tested surface treatments resulted in a decrease of the water contact angle. The dentin surface conditioned with phosphoric acid or phosphoric acid plus oxalate resulted in a significant increased in roughness and a decrease in nano-hardness. Ethylenediaminetetraacetic acid (EDTA) induced no significant changes in either the dentin surface roughness or the nano-hardness values. The three tested conditioned systems all showed similar bond strengths. Conclusions: Conditioning the dentin with EDTA improved the dentin wettability as a result of chemical surface modifications without altering the dentin nano-hardness. The EDTA-conditioned dentin surface may be suitable for resin bonding. The application of potassium oxalate after phosphoric acid etching did not alter the surface properties of the phosphoric acid etched dentin. (C) Koninklijke Brill NV, Leiden, 2012