Abstract: A bandpass filter based on resonant tunneling phenomenon in three-core photonic crystal fibers (PCFs) is presented. Resonance will occur if the effective refractive indices of the fundamental modes of three-core PCFs match at the same wavelength. By choosing the proper parameters of PCFs, all the three modes could meet the resonant condition. The effective refractive indices of the three-cores match only at the wavelength of 1.55m. As a result, wavelength-selective coupling is achieved. Full-vector beam propagation method (BPM) is employed to analyze the performance of the filter. Numerical investigation demonstrates that the coupling length is 22.8mm, and the bandwidth of the bandpass filter is 8.9nm with the loss of -3dB at 1.55m.