Oxide ion conductivity of Ga based perovskite type oxides, LnGaO(3) (Ln = Nd, La) and its related oxide, A(3)Ga(2)O(6) (A = Ba and St) was investigated. Oxide ion transference number is almost 1.0 on Sr3Ga2O6 or Ba3Ga2O6. However, electrical conductivity of these A(3)Ga(2)O(6) system oxides was lower than log (sigma/S cm(-1)) = -3 due to the low solubility of the aliovalent cations. On the other hand, doped perovskite type oxide of NdGaO3 and LaGaO3 exhibited a high electrical conductivity and the transference number of oxide ion was higher than 0.9 in the oxygen partial pressure range from P-O2 = 1 to 10(-21) atm. In particular, Ca and Mg doped NdGaO, exhibited a high oxide ion conductivity in similar with LaGaO3 based oxide.