The thermodynamic activity of Li2O in Li0.23La0.61TiO3 (LLT) was measured by an electrochemical galvanic cell using YSZ as the reference electrode to determine the phase boundary of reaction of different CO2 contents with Li2O in LLT to form Li2CO3. The Li2O activity in LLT was evaluated from the electromotive force (EMF) vs. log(P-CO2) plot. The lithium ion conductivity in LLT was investigated by AC impedance measurements and the bulk and grain-boundary conductivities were isolated by identifying the frequency-independent plateau regions on the capacitance bode-plot which showed two temperature-independent distinct plateaus associated with bulk and grain boundary response. The grain boundary conductivity was > 1 order of magnitude lower than that of the bulk and the activation energies for bulk and grain boundary lithium ion conduction were 0.47 +/- 0.01 and 0.77 +/- 0.02 eV. The Kohlrausch stretching parameter (beta) was calculated from the normalized plot of complex modulus (M '') vs. frequency.