A novel band-rejection filter based on a Bragg fiber with a defect layer is proposed.A defect layer is introduced in the periodic high/low index layers in the cladding of the Bragg fiber,which results in large confinement loss for some resonant wavelengths inside the band gap range of the Bragg fiber.A segment of the Bragg fiber with a defect layer can be used as a band-rejection filter,whose characteristics are mainly determined by the structure of the Bragg fiber.The simulation results show that the bandwidth of such a band-rejection filter is dependent on the number of the periodic high/low index layers in both sides of the defect layer in the cladding of the Bragg fiber. A novel band-rejection filter based on a Bragg fiber with a defect layer is proposed. A defect layer is introduced in the periodic high / low index layers in the cladding of the Bragg fiber, which results in large confinement loss for some of a the band gap range of the Bragg fiber. A segment of the Bragg fiber with a defect layer can be used as a band-rejection filter, whose characteristics are mainly determined by the structure of the Bragg fiber. The simulation results show that the bandwidth of such a band-rejection filter is dependent on the number of the periodic high / low index layers in both sides of the defect layer in the cladding of the Bragg fiber.