It may safely be said that Japan is a rainy area. But lately the problem of waterresources is felt more and more keenly and the relation of a drainage basin and water balance are rising in importance. Also，as the locus of our activity is expanding from level land to mountainous areas，the demand for water is increasing. Still more，the study of a water balance is becoming a necessity from both the viewpoints of prevention of warter-related damage in mountainous areas and of ecology. From this point of view，in this report. the characteristics，the engineering properties and water balance of a small drainage basin are described.