Background: The antileukemic activity of hot water extract of plant parts of some Japanese willow tree species grown at different levels of nitrogen were examined. Materials and Methods: Water extracts of willow leaves were prepared for this studies in different level of nitrogen nutrition. Results: The extracts obtained from the leaves and stem exhibited anti-leukemic activities prominently. The crude hot water extracts of the young growing parts including apex, matured leaves and stem, killed the blasts of acute myeloid leukemia (AML) cells, (HL60 and NB4) after 48h incubation, however, such desperation was far less in the root extract. Similar to the plant parts, response of extracts obtained from different willow species was not identical; the proportion of dead cells relative to whole cells of the culture medium ranged from 21% to 93% among the species. Leaf extracts obtained from the responsive willow species decreased the live cell percentage and increased the dead cell percentage at higher level of nitrogen nutrition. The mode of desperation of leaf extract treated AML cells in such species appeared to be cell apoptosis as shown by binding with fluorescein isothiocyanate (FITC) -labeled Annexin V. Conclusion: Differentiation of alive AML cells continued unabated and apoptosis was poor when extract of an unresponsive species added to the culture medium.