We investigated the usability of a trimming mechanism for varying an external quality factor (Q e ) in a hightemperature superconducting bandpass filter (BPF) using bulk resonators at around 5 GHz. The proposed trimming mechanism was composed of air space between an input port and the first resonator in a Cu cavity, a center conductor of the coaxial through the space, and a dielectric or metallic trimming rod. We decided the geometrical dimensions of the trimming mechanism and estimated the Q e by varying the height of rod (h Q ) using an electromagnetic simulator. These simulated results indicate that the proposed mechanism could function for theoretical Q e values up to those of 8-pole BPF. We then fabricated the trimming mechanism for Q e and measured the Q e by using a vector network analyzer. The measured data almost matched the simulated data. Next, we fabricated a 5-pole BPF with the trimming mechanisms for Q e and obtained good filtering responses.