The lowland dry evergreen forests have largely disappeared in other Indochina Peninsula countries under seasonal tropical climate, while an area of 32,000 km² remains in Cambodia. The large evergreen forests would have a decisive influence on regional water cycle via its transpiration during dry season. Dipterocarpus costatus is one of the major emergent tree species in Cambodian lowland dry evergreen forests, and is threaded by illegal logging for timber use. We measured intact leaf stomata conductance of D. costatus using leaf porometer (SC-1; DECAGON, USA) in Kampong Thom Province in central Cambodia during a dry season, from Dec. 2008 to Feb. 2009. Leaf stomatal conductance was high at 10 – 40 days after expanding (> 200 mmol m^-2 s^-1), and reached to the maximum at 30 – 40 days after expanding, and kept 40 – 50 % of the maximum value after 60 days (< 150 mmol m^-2 s^-1). Senescent leaves displayed low conductance 5 days before shedding. Transpiration potential per branch would be high at the beginning of January estimated from conductance data and leaf age composition in branches. Since D. costatus distinctively displays biannual leaf exchange at the beginning and end of dry season, a whole tree transpiration could peak twice in a year, at the mid of dry season and the beginning of rainy season.