This research deals with the catalytic behavior of the methane steam reforming reaction over a new Ni-exsolved Ruddlesden-Popper manganite during prolonged reaction time (up to 100 h) with special focus on the possible carbon deposition and H2S poisoning. La1.5Sr1.5Mn1.5Ni0.5O7±δ material was synthesized and reduced in diluted hydrogen to induce Ni exsolution. Its catalytic behavior in long reaction times was compared to Ni-impregnated manganite and Ni/YSZ cermet. The catalytic measurements for the steam reforming reaction were carried out at 850 °C in low steam-to-carbon conditions. All materials are susceptible to H2S poisoning (50 ppm), forming undesired sulfide compounds with damaging impact on their catalytic activity. In contrast, during tests without H2S, the activity for cermet and impregnated materials drops at relatively short reaction time due to coking formation, as evidenced by TEM and TGA/MS analysis, while the behavior of new exsolved material remains stable throughout the test. This high stability of the new exsolved catalyst over a prolonged reaction time is a noticeable advantage due to its potential use as SOFC anode fed with natural gas free of H2S.