Purpose: To evaluate the effects of saliva contamination on microtensile bond strengths of all-in-one adhesives to dentin. Materials and Methods: Flat superficial occlusal dentin surfaces of extracted human molars were used and randomly divided into 2 groups depending on two all-in-one adhesives: One-Up Bond F Plus (Tokuyama Dental) and Adper Prompt L-Pop (3M ESPE). For each adhesive, the teeth were allocated to 7 subgroups in which one group was bonded without contamination with saliva, serving as a control. The other groups, either before or after the polymerization of adhesives, were contaminated with saliva and dried; contaminated, dried, and adhesives re-applied; contaminated, rinsed, and the adhesives re-applied. Resin composite was then placed on the treated dentin surfaces. After 24 h storage in distilled water at 37°C, the teeth were sectioned perpendicular to the adhesive interface in x and y directions, obtaining multiple beam-shaped specimens with a cross-sectional area of approximately 1.0 mm2. Specimens were stressed in tension at 1 mm/min until rupture of the bond. Data were analyzed using one-way ANOVA and the Games-Howell test. Results: For both all-in-one adhesives, saliva-contaminated groups showed lower bond strengths than the controls. Re-application of the adhesives after drying or rinsing the saliva off restored the dentin bond strengths to the control levels. Conclusion: Saliva contamination reduced the dentin bond strengths of all-in-one adhesives. Supplementary application of the adhesive after cleaning the saliva from the dentin surface is an empirical recommendation for restoring bond strength. Keywords: all-in-one adhesive, bond strength, microtensile bond test, saliva contamination