Formation of the La2Cu1-xCoxO4+delta solid solutions with orthorhombic K2NiF4-type structure was found to be in the range of 0 less than or equal to x less than or equal to 0.30 at temperatures above 1270 K. Incorporating cobalt into the copper sublattice of lanthanum cuprate leads to increasing oxygen hyperstoichiometry and decreasing electrical conductivity. Thermal expansion coefficients of the La2Cu1-xCoxO4+delta (x = 0.02-0.30) ceramics at 470-1100 K were calculated from the dilatometric data to vary in the range (12.2-13.2) x 10(-6) K-1. Studying the dependence of oxygen permeation fluxes through La,Cu(Co)O4+delta on the membrane thickness demonstrated that the oxygen transport at the thickness values below 1 mm is limited by both surface exchange rate and bulk ionic conductivity. Oxygen permeability of the La2Cu1-xCoxO4+delta solid solutions was ascertained to increase with cobalt concentration at x = 0.02-0.10 and to decrease with further dopant additions, indicating a participation of interstitial oxygen in the ionic transport.