Decreasing temperature and increasing precipitation along altitude gradients are typical mountain climate in subtropical China. In such a climate regime, identifying the patterns of the C stable isotope composition (δ(13)C) in plants and soils and their relations to the context of climate change is essential. In this study, the patterns of δ(13)C variation were investigated for tree leaves, litters, and soils in the natural secondary forests at four altitudes (219, 405, 780, and 1268 m a.s.l.) in Lushan Mountain, central subtropical China. For the dominant trees, both leaf and leaf-litter δ(13)C decreased as altitude increased from low to high altitude, whereas surface soil δ(13)C increased. The lower leaf δ(13)C at high altitudes was associated with the high moisture-related discrimination, while the high soil δ(13)C is attributed to the low temperature-induced decay. At each altitude, soil δ(13)C became enriched with soil depth. Soil δ(13)C increased with soil C concentrations and altitude, but decreased with soil depth. A negative relationship was also found between O-alkyl C and δ(13)C in litter and soil, whereas a positive relationship was observed between aromatic C and δ(13)C. Lower temperature and higher moisture at high altitudes are the predominant control factors of δ(13)C variation in plants and soils. These results help understand C dynamics in the context of global warming.