The survival of mesenchymal stem cells (MSCs) to tumor necrosis factor α (TNFα) stimulation was evaluated after a long-term antioxidant treatment, or caloric restriction, in aged rats. MSCs were isolated from bone marrow of 30-month-old rats which orally received N-acetylcysteine in the last 18 months. The necrotic cell death-induced in vitro by TNFα, determined by trypan blue exclusion, was markedly attenuated in MSCs obtained from treated vs. control aged rats (percent mean ± SEM: 10.9 ± 2.17 vs. 17.8 ± 0.53; p < 0.05). Also, the proliferation rate of MSCs from control, but not N-acetylcysteine-treated, aged rats evaluated up to 2 weeks was significantly higher than that of MSCs from younger (4-month-old) rats. No significant effect was observed relative to the parameters investigated when the aged rats were previously subjected to a hypocaloric diet for 18 months. In conclusion, a prolonged supplementation with N-acetylcysteine in rats can increase resistance to necrotic death of MSCs and may also counteract an excessive rate of MSC proliferation.