Lianas usually possess large vessels which are vulnerable to cavitation. Root pressure may play an important role in embolism repair of vessels. However little is known about the generality of root pressure in tropical lianas. To characterize root pressure of lianas in tropical rainforests we used pressure transducers to measure root pressure in the rainy and dry seasons for a total of 32 lianas from 14 families common in Xishuangbanna. We further analyzed the associations of maximum root pressure with phylogeny and of transient root pressure with environmental factors. We found that all lianas we selected had root pressure with maximum root pressure ranging from 2-138kPa. In the dry season about 72% (23 species) of the lianas had relatively low root pressure (<15kPa) and maintained positive throughout the day. This may be important for water balance for roots and basal stems of lianas. There were three types of diurnal changes in liana root pressure. In Type I root pressure had obvious diurnal variation in the dry and rainy seasons. In Type II root pressure did not show obvious diurnal variation in the dry and rainy seasons. In Type III either in the dry or in the rainy season root pressure showed obvious diurnal variation. Root pressure varied substantially among lianas with lianas from two families Fabaceae and Vitaceae usually having relatively higher root pressure suggesting that phylogeny may influence root pressure. Transient root pressure closely responded to photosynthetically active radiation. In most cases however it was not related to rainfall and vapour pressure deficit. These results suggest that the associations of liana root pressure with environments need further investigation.