Objectives <p>This study aimed to compare the effects of alcohol-containing and alcohol-free mouthwashes on the surface roughness of bulk-fill composite resins. In this in-vitro, experimental study, 60 composite specimens measuring 6&#xa0;mm in diameter and 2&#xa0;mm in height were fabricated from Tetric N-Ceram and X-tra fil composite resins using a stainless-steel mold. After curing for 20&#xa0;s, the specimens were immersed in distilled water and incubated at 37&#xa0;°C for 24&#xa0;h. Baseline roughness was measured before dividing them into three groups for immersion in water, alcohol-containing, or alcohol-free Listerine for 24&#xa0;h, simulating two years of use. The specimens were then dried at room temperature, and their surface roughness was measured again. Data was analyzed by two-way ANOVA and t-test (α = 0.05).</p> Results <p>No significant change occurred in surface roughness of specimens after immersion in the respective solutions (<i>P</i> &gt; 0.05). The type of composite and the type of solution had no significant effect on the surface roughness of specimens (<i>P</i> &gt; 0.05). The results showed that Listerine alcohol-containing and alcohol-free mouthwashes had no significant effect on the surface roughness of the tested bulk-fill composite resins and no significant difference with each other in this respect.</p>