The seasonal meteorological conditions definitely dominate Water-Use efficiency (WUE) of dry dipterocarp forest ecosystem. It reveals an adaptation of plant physiology that is indicated by the relations between Water-Use and Gross Primary Production. This study aims to apply eddy covariance technique to estimate the seasonal Water-Used Efficiency of Dry Dipterocarp Forest during April 2013 to March 2014. The results show annual precipitation is 2.27 g C kg-1 H2O. The WUE are 2.38 and 2.11 g C kg-1 H2O in wet and dry season, respectively. The relative humidity strongly dominates WUE in wet season and vapor pressure deficit effect on WUE in dry season, compared to other meteorological variables. They are indicated by correlation coefficients of 0.57 and 0.91 for wet and dry season, respectively