Objective <p>To evaluate the effect of adding graphene oxide (GO) to HEMA-containing and HEMA-free universal adhesives on water sorption/solubility and bonding effectiveness to dentin.</p> Materials and methods <p>GO was incorporated into universal adhesives (Scotchbond Universal and G-Premio Bond) at three weight percentages (0.5, 1, and 3%) and characterized by SEM. Clearfil SE Bond was used as the reference adhesive. Disk-shaped specimens were prepared to evaluate water sorption and solubility (<i>n</i> = 10). Microspecimens were prepared from ninety extracted human third molar. The µTBS of half of the specimens was tested after 24&#xa0;h, and the remaining specimens were aged for 6 months. Failure mode was analyzed using a stereomicroscope. Statistical analyses were performed with one-way ANOVA, Duncan, and paired t-tests (<i>p</i> = 0.05).</p> Results <p>Adding 3% GO increased water sorption of the adhesives (<i>p</i> &lt; 0.05). Clearfil SE Bond exhibited the lowest water sorption and solubility (<i>p</i> &lt; 0.05). 1% GO significantly increased the immediate µTBS of the adhesives, whereas 3% resulted in a significant decrease (<i>p</i> &lt; 0.05). 0.5 and 1% GO significantly increased the aged µTBS of Scotchbond Universal, while only 1% improved the aged µTBS of G-Premio Bond (<i>p</i> &lt; 0.05). 3% GO reduced the aged µTBS of the adhesives (<i>p</i> &lt; 0.05). The highest immediate and aged µTBS were recorded for Clearfil SE Bond (<i>p</i> &lt; 0.05).</p> Conclusions <p>The bonding performance of universal adhesives improved with 0.5% and 1% GO additions, whereas 3% GO had a detrimental effect on both bond strength and water sorption.</p> Clinical significance <p>Adding GO to adhesives may improve the long-term durability of bonded restorations.</p>