The use of greenhouses has rapidly increased after 1965, and the area became 11 times of 1965 as of 2001. Meteorological conditions and soil moisture environments inside a greenhouse are significantly different from those in the open field. These differences should be understandable to establish accurate predictions of water consumption and evapotranspiration inside a greenhouse which play important roles in the design of any irrigation system. This study aims to estimate the micrometeorological conditions inside an oriental pickling melon greenhouse which can be used for evapotranspiration calculations. Therefore, micrometeorological data were measured inside and outside the greenhouse for the comparison purposes. The results of this study may be summarized as: (1) Solar radiation inside the greenhouse was decreased about 30% of that of outside it by plastic film and frame. (2) Net radiation during the daytime inside the greenhouse was almost the same as the absorbed total short-wave radiation. (3) The difference of daytime mean air temperature inside and outside the greenhouse was between 3 and 4 degree Celsius in day average. (4) Both relative humidity and saturation deficit inside the greenhouse were higher than outside, and those were affected by ventilation. (5) Wind speed inside the greenhouse was greatly affected by opening rate of the house side.