This study was conducted to compare the bond strength of etch-and-rinse “Adper Single Bond 2” (3M ESPE) and self-etch adhesive system “Single Bond Universal” (3M ESPE) before and after application of two desensitizing agent: glutaraldehyde based “Telio” (Ivoclar Vivadent) and hydroxyapatite nanoparticles bonded to superficial and deep dentin.Thirty freshly extracted human molars were utilized in this study for micro-shear bond strength testing. Each molar was sectioned in order to obtain dentin specimens at two depths: superficial dentin at 0.5mm below the dentino-enamel junction (DEJ) and deep dentin at 1.5mm below the DEJ resulting in 60 specimens (30 each depth). Each dentin specimen was divided into two halves according to the adhesive system used, then divided into three subgroups according to the surface treatment into control (no treatment), hydroxyapatite nanoparticles and glutaraldehyde based desensitizing agent.Micro-shear bond strength test was carried out by using translucent microtubules with an internal diameter of 1 mm and 1 mm height. The microtubules were placed on the prepared dentin specimen to be filled with the composite resin material “Filtek Z350XT” (3M ESPE) after application of desensitizing agents and the adhesive systems. All specimens were stored in distilled water for 24 hours. Micro-shear bond strength was assessed using a universal testing machine in a pull motion. Environmental Scanning electron microscope