The transmission properties of defect modes for a doped one-dimensional photonic crystal (1DPC) surrounded by an μ-negative layer and a μ-negative layer are studied. The reflection phase spectra of μ-negative and a μ-negative media and the transmission phase spectra of the doped 1DPC are calculated by means of the transfer matrix method. It is found that the sum of the reflection phases of μ-negative and a μ-negative layers and the double transmission phases of the doped 1DPC under special conditions are zero or integer multiple of 2π.The results show that only one defect mode appears in the photonic gap when the doped 1DPC surrounded by an μ--negative layer and a μ-negative layer, regardless of the thickness of the defect. Moreover, the quality factor of the single defect mode is enhanced greatly due to the confinement effect of the ε-and μ-negative layers.