The microring resonator (MRR) plays an important role in signal processing because high-quality bandpass filtering can be obtained at its drop port. To promote the signal-to-noise ratio, a high rejection ratio is significantly demanded. However, it is still challenging to promote the rejection ratio of the MRR-based bandpass filter. To solve this problem, we propose to use an all-pass filter to enhance the rejection ratio of the MRR-based bandpass filter. Experimental results show that the improved rejection ratio is as high as 47.7 dB, which is improved by 23.6 dB compared with that of the MRR. Meanwhile, the bandwidth of the MRR-based bandpass filter is reduced from 2.61 to 1.14 GHz due to the constructive interference in the passband. In addition, the center frequency of this ultrahigh rejection MRR can be continuously tuned from 6.26 to 46.25 GHz. The quality factor (Q) of the MRR is improved from 7.4 × 10 4 to 1.7 × 10 5 . During the adjustment, the rejection ratio of the bandpass filter exceeds 40 dB. The proposed approach can be used to achieve optical bandpass filters with high performance.