In situ XRD studies have been performed on La-Ni-Al-O catalysts for CO2 reforming of methane. Conditions were chosen to get information about catalysts used in fluidized bed reactors. Gas products were monitored by mass spectrometry. Reduction and catalytic properties of model compounds like LaNiO3 and LaNiAl11O19 as well as catalysts containing mixtures of such oxides were studied. Introduction of aluminium into the perovskite structure of LaNi1-xAlxO3 stabilizes the Ni-ions and a higher reduction temperature is necessary to obtain complete reduction to Ni(s), The magnetoplumbite type oxide, LaNiAl11O19, is reduced with even more difficulty. Furthermore, a continuous reduction of nickel is possible during the catalytic testing, stemming from such Ni-containing perovskite and magnetoplumbite type oxides of the catalyst. The reduced catalyst can be regenerated with O-2, however, the oxidation of Ni(s) is not complete under the chosen conditions. Treatment of the catalyst in CO, increases the activity of the catalyst and is probably due to removal of coke and formation of NiO which is immediately reduced during catalytic testing giving redispersed and more available Ni. The results clearly indicate that Ni is the active phase in CO, reforming of methane. By the methods used, no formation of La2O2CO3 was observed on the rested catalysts and the deactivation due to such compound could not be concluded. The results indicate dissolution of C in Ni under CO2 reforming conditions as a possible reason for deactivation.