Background <p>To investigated the combined effect of adhesive type and film thickness on dentin bond strength by comparing one and two-step universal adhesives applied in single and double layers.</p> Methods <p>Forty caries-free human third molars were collected and standardized Class I cavities were prepared. Specimens were restored using one-step (Clearfil Tri-S Bond Universal, Japan) and two-step (G2-Bond Universal, Japan) universal adhesive systems. Each group was subdivided into single and double-layer applications, light-cured, and restored with a universal composite resin. Sticks with a cross-sectional 1 × 1&#xa0;mm² were prepared for testing. Adhesive film thickness was measured under a stereomicroscope at ×80 magnification. Micro-tensile bond strength (µTBS) was evaluated either immediately or after 5000 thermocycles (TC). Failure modes were assessed under ×40 magnification. Wilcoxon Signed Ranks Test was used for paired comparisons of immediate and after TC tensile bond strengths. Mann–Whitney U test compared single vs. double layers of the adhesives. For adhesive film thickness, Independent Samples t-test was applied for group comparisons (<i>p</i> &lt; 0.05).</p> Results <p>Double-layer application produced significantly thicker adhesive films for Clearfil Tri-S Bond and G2-Bond Universal compared with single-layer application (<i>p</i> &lt; 0.05). However, no significant differences in µTBS were observed between single and double-layer groups of either adhesive, regardless of aging. Thermocycling significantly reduced bond strength for both systems (<i>p</i> &lt; 0.05). Overall, the two-step adhesive demonstrated higher µTBS values than the one-step adhesive.</p> Conclusion <p>Although double-layer application increased adhesive film thickness, it did not improve dentin bond strength. The two-step universal adhesive system showed superior bonding performance compared with the one-step system, both immediately and after thermocycling.</p>