A fossil leaf identified as Carpinus miofangiana Hu et Chaney was discovered in the Late Pliocene sediments of the Mangbang Formation, Tengchong Country, Yunnan Province, China. It was well preserved with gross morphological structure and microstructure of cuticles in situ. The gross morphological characteristics of it were similar to that of the fossil species Carpinus miofangiana from the Shanwang Formation in Shandong Province: both of them are oblong-ovate, base obliquely cordate, leaf margin doubly minutely serrate. Their primary veins are straight and moderately thick, secondary veins are pinnate. Additionally, the anatomical characteristics of the present specimen are investigated here and compared with the modern leaf Carpinus fangiana, it is more credible to decide the taxonomic position of fossil plant using leaf architecture and cuticular characteristics together. As both the fossil and modern species shared similar ecological habits and clearly possessed very similar gross morphological characteristics and epidermic features, Carpinus fangiana was selected to be the fossil species’s nearest living equivalent species for comparative study in stomatal index. Consequently, the palaeo-atmospheric CO2 concentration, 464ppmv, was estimated based on stomatal ratio approach. The result was consistent with the CO2 value of Berner’s global carbon budget model (GEOCARB III). It therefore suggested that the leaf of Carpinus miofangiana can be a good proxy for palaeo-CO2 levels. Based on the comparing in cuticular characteristics between the fossil and the modern leaves, it can be inferred that the climate was warmer and more humid in the Pliocene of western Yunnan than that of the present.