WO3-doped Bi2O3 was found to exhibit stable fluorite-based structure. However, the electrical conductivity of WO 3-doped Bi2O3 is significantly lower than that of Y2O3-doped Bi2O3. The structure and electrical conductivity of samples formulated as (YXW 0.15Bi0.85-X)2O3.45 (X=0.1∼0.4) were investigated. The assintered (Y0.1W0.15Bi 0.75)2O3.45 exhibited a single cubic structure that is isostructural with δ-Bi2O3. However, the cubic fluorite structure may decompose into cubic structure and rhombohedral Y6WO12 after heat-treatment at 900°C for 3 hours. For X=0 2, 0.3 and 0.4, the as-sintered samples consisted of a cubic fluorite structure and rhombohedral Y6WO12. The conductivities of (YXW0.15Bi0.85-X)2O3.45 45 (X=0.1-0.4) decrease with increasing X value. For X=0.1, the conductivity is 1.97 × 10-3 S cm-1 at 700°C and slightly lower than that of (W0.15Bi0.85)2O3.45. The Bi 6s2 lone pairs of electrons are known to lead to enough oxygen ion mobility. Thus it is reasonable to expect that ionic conductivity drops as Y substitutes for Bi.