A comparative investigation of the much-studied La 2 NiO 4+δ (n=1) phase and the higher-order Ruddlesden-Popper phases, La n+1 Ni n O 3n+1 (n=2 and 3), has been undertaken to determine their suitability as cathodes for intermediate-temperature solid-oxide fuel cells. As n is increased, a structural phase transition is observed from tetragonal I4/mmm in the hyperstoichiometric La 2 NiO 4.15 (n=1) to orthorhombic Fmmm in the oxygen-deficient phases, La 3 Ni 2 O 6.95 (n=2) and La 4 Ni 3 O 9.78 (n=3). High temperature d.c. electrical conductivity measurements reveal a dramatic increase in overall values from n=1, 2 to 3 with metallic behavior observed for La 4 Ni 3 O 9.78 . Impedance spectroscopy measurements on symmetrical cells with La 0.9 Sr 0.10 Ga 0.80 Mg 0.20 O 3−δ (LSGM-9182) as the electrolyte show a systematic improvement in the electrode performance from La 2 NiO 4.15 to La 4 Ni 3 O 9.78 with ∼1 Ω cm 2 observed at 1073 K for the latter. Long-term thermal stability tests show no impurity formation when La 3 Ni 2 O 6.95 and La 4 Ni 3 O 9.78 are heated at 1123 K for 2 weeks in air, in contrast to previously reported data for La 2 NiO 4.15 . The relative thermal expansion coefficients of La 3 Ni 2 O 6.95 and La 4 Ni 3 O 9.78 were found to be similar at ∼13.2×10 −6 K −1 from 348 K to 1173 K in air compared to 13.8×10 −6 K −1 for La 2 NiO 4.15 . Taken together, these observations suggest favourable use for the n=2 and 3 phases as cathodes in intermediate-temperature solid-oxide fuel cells when compared to the much-studied La 2 NiO 4+δ (n=1) phase.