To understand the vegetation succession and climaticchanges at the southeastern margin of the TibetanPlateau in the Neogene, we reconstructed the Middle Miocene vegetation and climate based on palynological data from four localities, which are at different latitudes along the Ailao Mountains in Yunnan, southwest China. The palynological assemblages suggest that the vegetation there was composed of mixed evergreen and deciduous broad-leaved forests growing under subtropical conditions. Based on the palynological data, the palaeoclimatic parameters from the four localities are established. The new parameters were compared with those of the Late Miocene, of the Late Pliocene, and of today. The comparison revealed that the temperatures were obviously lower in the Middle Miocene than they are today. This suggested that the Ailao Mountains were not high enough to block the Asian Winter Monsoon in the Middle Miocene. The Middle Miocene vegetation at the southeastern edge of the TibetanPlateau was also compared to that of Central Tibet. It would appear that the palaeoclimate at the southeastern edge of the TibetanPlateau was warmer and wetter than in Central Tibet. In contrast to the Neogene cooling in Central Europe, the climate at the southeastern edge of the TibetanPlateau has gradually warmed since the Middle Miocene. This phenomenon was most likely caused by the uplift of the TibetanPlateau, which has succeeded in blocking the Asian Winter Monsoon since the Middle Miocene.