Tropical rainforests in Borneo Island sometimes have suffered from some drought coinciding with El-Niño. Understanding of drought impacts on the Bornean tropical forest trees is essential for assessing potential impacts of extreme weather events. This study was conducted to clarify tree water use and vertical partitioning of water uptake in response to soil drought in emergent trees in a Bornean tropical forest based on throughfall reduction experiments. We evaluated effect of experimentally reduced throughfall tree sap flux in three emergent trees with two control trees. As well, stable isotope analysis (natural abundance of delta18O) was used to assess depth of water uptake of the emergent trees. Soil water content was successfully reduced down to a soil depth of at least 0.8 m. Contrary to our expectation; we measured insignificant changes in sap flux in the emergent trees. Isotopic analysis suggested water uptake from deep soil water at < 0.8 m mitigated the soil drought. Simple soil water balance calculation suggested no-rainfall during the 60-90 days was acceptable for trees with rooting depth of 2 m.