The effect of Li2O-doping on solid-solid interaction, surface and catalytic properties Of Co3O4-MoO3/Al2O3 system were investigated using XRD, XPS, nitrogen adsorption at -196degreesC and oxidation of CO by O-2 at 100-300degreesC. The nominal composition of the system was 0.2 Co3O4-0.05 MoO3/Al2O3 and the amount of dopant was varied between 0.14 and 0.57 wt.% Li2O. The results revealed that Li2O-doping inhibited the formation of CoAl2O4 and CoMoO4 in the treated solids precalcined at 800degreesC and decreased the degree of crystallinity Of Co3O4. Also, Li2O-doping of the investigated system decreased the surface concentration of cobalt species and increased that of molybdenum species. The specific surface areas of the doped adsorbents precalcined at 600, 800 and 1000degreesC decreased progressively as a function of the amount of dopant added. The catalytic activities of pure and doped solids, in CO oxidation by O-2, decreased progressively by increasing the precalcination temperature in the range 600-1000degreesC. The doping process brought about a significant increase in the catalytic activities of the solids investigated due to an effective hindrance of formation of CoAl2O4 and CoMoO4 which exhibit catalytic activities smaller than that Of Co3O4. Lithia-doping of the investigated system did not modify the mechanism of the catalytic reaction but changed the concentration of catalytically active constituents without changing their energetic nature.