Aluminum trioxide (Al2O3) nanoparticles (NPs) loaded in a fifth-generation adhesive to caries-affected dentin. Molars with occlusal caries were selected. Specimens underwent acid etching and were categorized into 4 groups based on the concentration of Al2O3 NPs in the fifth-generation adhesive. Group 1: 0% Al2O3 NPs, Group 2: 2% Al2O3 NPs, Group 3: 5% Al2O3 NPs and Group 4: 10% Al2O3 NPs. Surface characterization of Al2O3 NPs was assessed via SEM, elemental distribution of particles in Al2O3 was evaluated via EDX, DC was assessed via FTIR, and antimicrobial efficacy was evaluated through the pour plate method. Teeth underwent μTBS testing using the universal testing machine. The Kruskal-Wallis test was used to assess the difference in survival rates of S. mutans. The means of different groups were compared using ANOVA and Tukey’s posthoc test to ascertain significant differences. The highest DC was observed in unmodified adhesive. The lowest DC was displayed in group 4. The highest μTBS scores were observed in group 3 samples. The lowest μTBS was observed in group 1 samples. The most effective group against S. mutans was 4. The ER adhesive loaded with 2 wt% and 5 wt% Al2O3 NPs exhibited superior μTBS and antibacterial effectiveness. The addition of Al2O3 to the adhesive resulted in a reduction in the degree of conversion.