The development of greenhouse culture in Japan is outstanding. In 1992 the total greenhouse area reached to 58, 300ha. Consumptive use of water inside the greenhouses are not studied enough inspite of the development of greenhouse culture. In this paper, we discussed about the characteristic features of meterological conditions related to evapotranspiration, refering to the data observed in closed and partly opened greenhouses. Regression coefficients were calculated on humidity, temperature, solar radiation and windspeed between the inside and the outside of greenhouse. The meteorological factors in the partly opened greenhouse showed higher regression than the factors in the closed condition. Solar radiation showed the highest regression with the pan evaporationin both closed and partly opened conditions. The applicability of Penman method was examined on estimating potential evapotranspiration in greenhouse. In the closed condition, pan evaporation data showed good agreement with Penman method but the data was 2 times higher than Penman method in the partly opened condition. These results shows that potential evapotranspiration is able to be estimated by Penman method, when windspeed is extremely low as in closed greenhouse. When convective conditions are affected by outside wind, Penman method has some difficulties in application, as wind term in the Penman equation include empirical constant derived from open field observation. The observed results shows pan evaporation is a good indicator on potential evapotranspiration, although it is affected by diameter, color, height, place and so on.