Porous Pt-YSZ composites were prepared by impregnation of a commercial YSZ powder by a platinic precursor (H2PtCl6) followed by isostatic pressing and sintering at 1000 degreesC. Two different contents of platinum were introduced, i.e., 1 and 5 wt.%. Electrical and electrochemical properties of these samples were investigated between 350 and 600 degreesC by using impedance spectroscopy under various atmospheres including He, O-2/He, and C3H8/O-2/He. The catalytic activity of these samples for the propane combustion has also been investigated in the same temperature range. Dispersed platinum particles in YSZ at the surface of YSZ grains acted as an additional blocker of the ionic conductivity. This additional grain boundary was ascribed to the formation of platinum oxides or of a layer of chemisorbed oxygen on dispersed Pt particles. The interfacial process seemed to be characterized by a predominant low-frequency contribution, whatever the temperature, the Pt loading, and the atmosphere. This contribution was interpreted in terms of an oxygen concentration polarization. It was found to vary in the same way as the grain boundary process. The catalytic performances of porous Pt-YSZ composites for propane combustion were higher than those of Pt films deposited on a dense YSZ pellet. Unfortunately, we did not evidence any electrochemical promotion of the catalytic activity in our operating conditions. (C) 2004 Elsevier B.V. All rights reserved.