The effect of the precipitation conditions on the catalytic and structural properties of LaMnO3+delta, LaCoO3-delta and LaCo1-yMnyO3+/-delta perovskites (y = 0.33, 0.5, 0.67) has been studied by means of powder X-ray diffraction, temperature programmed oxygen desorption, textural measurements and catalytic activity measurements in methane total oxidation, Ageing time of the precipitate and H2O2 content in the precipitant influences crystallinity and phase composition of the perovskite samples pretreated at 600 and 800 degrees C. The results of the catalytic activity are affected by the presence of oxide admixtures and crystallinity.