Introduction: The aim of this study was to evaluate whether hemostatic agents containing aluminum chloride affect the microtensile bond strength of a universal adhesive to dentin. Materials and Methods: The occlusal enamel of 50 human molars was removed to expose a flat dentin surface. A universal adhesive was applied either in self-etch (SE) or etch & rinse mode (ER), or a contamination with a "hemostatic agent" (Astringent; ARP or Racegel; RAC) was performed prior to the adhesive application. In the control group (control; C), no contamination in SE and ER mode was performed. A composite build-up was placed onto the adhesively pre-treated surface and specimens were cut to obtain 80 microsticks per group. Half of the specimens were stored for 24 hours before the microtensile bond strength test was performed, the other half was tested after thermocycling (TC, 5,000 cycles). The fractured surfaces were evaluated using a light-optical microscope in order to analyze the failure pattern. Results: In the SE-mode, dentin contamination with both hemostatic agents prior to universal adhesive application led to a significant decrease in bond strength, compared to the controls before (SE_ARP: 5.67 ± 7.64 MPa; SE_RAC: 5.08 ± 6.04 MPa vs. SE_C: 24.91 ± 12.06 MPa) and after TC (SE_ARP_TC: 2.38 ± 4.43 MPa; SE_RAC_TC: 4.01 ± 4.42 MPa vs. SE_C_TC 24.27 ± 10.67 MPa). Moreover, the SE-mode with prior contamination showed significantly lower bond strength values to dentin before (SE_ARP 5.67 ± 7.64 MPa vs. ER_ARP 20.90 ± 10.91 MPa and SE_RAC 5.08 ± 6.04 MPa vs. ER_RAC 25.62 ± 9.41 MPa) and after TC (SE_ARP_TC 2.38 ± 4.43 MPa vs. ER_ARP_TC 20.91 ± 11.21 MPa and SE_RAC_TC 4.01 ± 4.42 MPa vs. ER_RAC_TC 18.94 ± 9.54 MPa) compared to the ER-mode. In the ER-mode, only contamination with ARP led to a significantly lower bond strength compared to uncontaminated dentin before TC. The fracture analysis showed significant more adhesive fractures in the SE-mode than in the ER-mode. Conclusion: Considering the limitations of this in-vitro study, the universal adhesive showed higher dentin bond strength when used in ER-mode after contamination with an aluminum chloride-based hemostatic agent. Palabras clave: dentin, hemostatic agent, microtensile bond strength, universal adhesive