From the standpoint of water resources development and environmental preservation, rain water retentivity of agricultural and forest lands are evaluated. Measurement of rainfall and runoff has been carried out at the reclaimed upland field of 4.55 ha since 1981. In this article, water retention characteristics of this study basin is compared in a rainy year of 1993 and a droughty year of 1994. In cases of rainfall less than 20mm, most of the rain water infiltrates into the soil layer. On the other hand, about 75% of a heavy rain, such as 300 mm in 1993, runs off the soil surface. Within the infiltrating rain water, the ratio of water which is kept by capillary action and can be used by crops is estimated to be less than 40% in months of rainfall more than 150 mm, but in months of rainfall less than 50 mm, it is estimated that more than 80% of rainfall can be used by crops. The ratio of monthly rainfall which contributes to base flow recharge is 0 to 12% regardless of rainfall amount.