INTRODUCTION: Many advances in flowable composites have been developed in the last few years, including the introduction of selfadhering flowable composites (SAFCs) that do not require the application of adhesive systems. OBJECTIVES: The objective of this study was to evaluate the influence of preliminary etching with 37% phosphoric acid on the shear bond strengths of two SAFCs (Vertise Flow and Fusio Liquid Dentin) to dentin. MATERIALS AND METHODS: Sixty sound human permanent molars were collected and prepared to expose the mid-coronal dentin. Dentin specimens were randomly divided into six groups (n=10) according to the material applied: (1) Vertise Flow (VF); (2) Fusio Liquid Dentin (FLD); (3) Gel Etchant/Vertise Flow (GE/VF); (4) Gel Etchant/Fusio Liquid Dentin (GE/FLD); (5) Optibond all-in-one/Premise Flowable (Opti-A/PF); (6) Gel Etchant/ Optibond all-in-one/Premise Flowable (GE/Opti-A/PF). Specimens were subjected to shear bond strength (SBS) test. Failure modes were evaluated under stereomicroscope and assessed using Adhesive Remnant Index (ARI) scores. Data were collected and statistically analyzed using ANOVA F-test and Chi-square test (p < 0.05). RESULTS: Group 6 (GE/Opti-A/PF) recorded the highest mean SBS (16.39 ± 2.418 MPa), while Group 1 (VF) recorded the lowest mean SBS (4.32 ± 0.993 MPa). The one-step self-etch adhesive Optibond all-in-one with and without a separate etching step had significantly higher mean SBS than those of the two SAFCs. Preliminary etching of dentin significantly increased the SBS of only Vertise Flow. CONCLUSIONS: The bonding performance of the 1-step self-etch adhesive (SEA) (Opti-A) was considerably better than those of the two SAFCs. Preliminary acid etching of dentin enhances the bonding performance of VF.