A series of compositions Yb_1-xBi_xO_1.5 (0.0 ≤ x ≤ 1.0) were prepared and characterized by X-ray diffraction, Raman spectroscopy, Scanning electron microscopy and ac-impedance spectroscopy. The XRD and Raman spectroscopic studies revealed that all the compositions, except x = 0.00 exist as a mixture of feebly Bi₂O₃ doped cubic Yb₂O₃ and heavily Yb₂O₃ doped fluorite type Bi₂O₃ phases. The presence of distortion around the Bi³⁺ in the fluorite type Bi₂O₃ is observed from the Raman spectroscopic studies. The uniform distribution of these two coexisting phases is observed in their SEM images. At around 673 K, the ac-impedance measurements revealed appreciable ionic conductivities for compositions with x≥0.05. The activation energies for conduction were in the range of 1.1–1.4 eV. The temperature and composition dependent conductivities have been explained on the basis of increased contributions of grain boundaries and fluorite type δ-Bi₂O₃ phase.