Leaf carbon isotope composition (δ13C) of both vascular and non-vascular plants were investigated in order to assess their variability along an altitude gradient (414, 620, 850, 1086,1286 and 1462 m) from a subtropical monsoon forest located at Mt. Tianmu Reserve, eastern China. Leaf δ13C values of all plant species ranged from -34.4 to -26.6‰, with an average of -29.8‰. There is no significant difference in leaf δ13C between vascular plants and mosses, however, trees had significantly higher δ13C values than herbs. For pooled data, leaf δ13C was positively correlated with altitude. Leaf δ13C was significantly and negatively correlated with annual mean temperature and atmospheric pressure, while it was significantly and positively correlated with soil water content. Furthermore, there was no relationship between leaf δ13C and soil nitrogen content or soil phosphorus content. The altitudinal trend in leaf δ13C is the consequence of the interaction between temperature, atmospheric pressure and soil water content.