Yttria-stabilized zirconia (YSZ) electrolyte disks with patterned Sr-doped LaMnO 3 (LSM) electrodes having different three-phase boundary (TPB) lengths (l T P B ), but the same electrode-electrolyte interface area, were prepared using photomicrolithography. Impedance spectra for half-cells were obtained under oxygen partial pressures; p O 2 , ranging from 10 - 3 to 1 atm and temperatures from 650 to 800°C. Area specific charge-transfer resistance, R c t , was found to vary inversely with l T P B . While the charge-transfer resistance is inversely proportional to l T P B . consistent with the charge-transfer reaction occurring mainly at the TPB, at 800°C some transport through LSM also appears to occur. The estimated value of charge-transfer resistivity, p c t , corresponding to the charge-transfer reaction occurring at the TPB in air at 800°C (1.26 x 10 5 Ω cm), is in good agreement with that estimated from actual fuel cell tests using quantitative stereological analysis of LSM-YSZ composite electrodes. R c t and ρ c t were found to decrease with increasing p O 2 and with increasing temperature. The activation energy for the overall charge-transfer reaction was estimated to be ∼1.5 eV.