Understating of the water availability and its corresponding use by Mallotusphilippensis and its control by climatic factors can give an idea about the ecosystem interaction. The sap flow measurement taken in M. philippensis during 2014 in Barkot forest showed that,the sap flow rate varied with time of day and season and also with radial depth of the tree trunk. The average daily sap flow rate was found to be 11.5 ± 1.7 cm h-1. Month-wise daily sap flow rate ranged between 4.4 to 10.6 cm h-1in outer portion of the trunk and 12.7 to 17.7cm h-1 in the inner portion of the trunk. Night-time sap flow contributed about 44 per cent of the total annual sap flow. Relative humidity was found to have slightly higher effect on diurnal sap flow rate than air temperature. Monthly sap flow was found to be a function of air temperature. The sap flow rate obtained during this study will be used in augmenting carbon flux studies being carried out in Barkot Flux site (BFS) and can be used in development of canopy conductance and stand transpiration models and validations.