Introduction: The present study was done to evaluate microbial adhesion on the critical surface of different brackets. Objectives: Evaluation of microbial adhesion on the critical surface of different brackets. Methods: The study was conducted on ten different types of commercially available orthodontic brackets. They were catego-rized into Group 1 and Group 2. Twenty-five MBT (0.22×0.28 slot) upper right premolar brackets were tested in each group. All the brackets were tested without any kind of ligation. CFU was calculated in both groups. Results: Adhesion of aerobic bacteria to Group I brackets are statistically significant (p<0.001). Adhesion of aerobic bacteria to Group II brackets was statistically significant (p<0.001). Adhesion of anaerobic bacteria to Group I was not statistically significant (p>0.05). Adhesion of anaerobes to Group II brackets was statistically significant (p<0.001). Adhesion of anaerobic bacteria is higher in Group II E (46.60) followed by Group II D (42.00), Group II C (37.20), Group IIB (28.04), Group IIA (28.20). The comparison of adhesion of aerobic and anaerobic bacteria to Group I brackets was not statistically significant in Group I B, IC (P>0.05). Statistically, significant correlation found between Group IA, ID, IE brackets towards affinity of aerobic and anaerobic bacteria. Adhesion of aerobic and anaerobic bacteria to Group II brackets were statistically significant (p<0.001). Conclusion: On comparison of aerobes and anaerobes present study was found that significant correlation between adhesion of aerobes to Group I & II brackets whereas no significant correlation found between adhesion of aerobes & anaerobes to Group IB & IC brackets. © 2021 Elsevier B.V., All rights reserved.