Objective: This study aimed to compare the effects of passive self-ligating (PSL) and conventional ligating (CL) of brackets onthe buccolingual inclination (BLINC) of the maxillary premolars.Methods: This in vitro study included a PSL bracket group and a CL bracket group. Acrylic teeth on typodonts were aligned using 0.014-inch heat-activated nickel titanium (HANT) (T1) and 0.019×0.025-inch HANT (T2) and 0.021×0.025-inch stainless steel(SS) (T3) archwires in a sequence. Standardized cone beam computed tomography (CBCT) images were taken immediately aftereach archwire stage. The differences of premolar teeth BLINC values in the 0.019×0.025-inch and 0.014-inch HANT archwires(T2-T1) and 0.021×0.025-inch SS and 0.019×0.025-inch HANT archwires (T3-T2) were compared between PSL and CL groups. Thevalue of p < 0.05 was considered statistically significant.Results: The BLINC change of the second premolar (SPM) showed a statistically significant difference (p=0.008), but the BLINCchange of the first premolar (FPM) (p=0.056) between the groups showed no statistically significant difference during the T2-T1 stage. However, there were statistically significant differences between two groups in the BLINC of the FPM (p=0.032) andSPM (p=0.032) in the T3-T2 stage. The angular changes in the buccal direction in the PSL group were higher than those in theCL group.Conclusion: The PSL upper premolar brackets used with the 0.021×0.025-inch SS archwire produced more buccal crown movement of the upper PM teeth compared with that of the CL brackets.