This paper presents a novel microstrip feedline structure to introduce an extra and controllable transmission zero (TZ) with high rejection for a narrowband filter.This structure loads a reconfigurable capacitor at the end of the input feedline without changing the main structure of the filter.The capacitor is recognized by a 2-bit inter-digital capacitor array.The asymmetrical microstrip feedline structure is suitable for multiple-pole filter designs.A low-loss six-pole high-temperature superconducting bandpass filter with a reconfigurable TZ is designed and fabricated.The center frequency of the filter is 5.22 GHz with TZ at the lower stopband.The TZ can be tuned among four different states.The out-of-band rejection at the TZ frequency is higher than 90 dB,and the insertion loss is lower than 0.92 dB.The measured results are consistent with the simulations.