The invention concerns a composition for purifying exhaust gases of an internal combustion engine capable of consuming fuel with lean air-fuel ratios comprising means adsorbing the NOx present in the exhaust gases, in the presence of excess oxygen and releasing the adsorbed NOx when the oxygen concentration of the exhaust gases decreases. The invention is characterised in that the NOx adsorbing means comprise in combination: a first composition comprising a support and an active phase, the active base being based on manganese and at least another element A selected among alkalines and alkaline-earths, the manganese and element A being chemically bound; a second composition comprising a support and an active phase based on manganese and at least another element B selected among alkalines, alkaline-earths and rare earths, said second composition having or being capable of having a specific surface area of at least 80 m /g after being calcined at 800 DEG C, and furthermore, a reducing and/or three-way catalyst function is incorporated in the NOx adsorbing means.