Yttria-stabilized zirconia (YSZ) electrolyte disks with patterned Sr-doped LaMnO3 (LSM) electrodes having different three-phase boundary (TPB) lengths (l(TPB)), but the same electrode-electrolyte interface area, were prepared using photomicrolithography. Impedance spectra for half-cells were obtained under oxygen partial pressures; p(O2), ranging from 10(-3) to 1 atm and temperatures from 650 to 800degreesC. Area specific charge-transfer resistance, R-ct, was found to vary inversely with l(TPB). While the charge-transfer resistance is inversely proportional to l(TPB), consistent with the charge-transfer reaction occurring mainly at the TPB, at 800degreesC some transport through LSM also appears to occur. The estimated value of charge-transfer resistivity, rho(ct), corresponding to the charge-transfer reaction occurring at the TPB in air at 800degreesC (1.26 x 10(5) Omega cm), is in good agreement with that estimated from actual fuel cell tests using quantitative stereological analysis of LSM-YSZ composite electrodes. R-ct and rho(ct) were found to decrease with increasing p(O2) and with increasing temperature. The activation energy for the overall charge-transfer reaction was estimated to be; 1.5 eV. (C) 2005 The Electrochemical Society.